How cheaply have you don’t the PCT

Brain fart, too much planning today.

I was probably on the low end, no clue because I didn't keep track. But there are certainly things you can do to minimize expenses.
1) Follow Scott williamsons advice and live on the trail, not in town. The more time you spend in town the more you'll spend..
2) Food. This is a tough one but if you are experienced then mail drops could save you money. But know what you will eat. If you are wrong then you double spend on all the food you don't eat from your resupply.
3) start later. If you start early then you will increase your likelihood of early season storms encouraging you to go into town.
4) go faster. I hiked the trail fast and this cut down both on zeros and overall hiking days. It can also help you further north since you can finish earlier, the earlier you finish the less rain and possibly snow up north.
5) find other budget conscious hikers. If you are part of a free spend group you will have pressure to spend more time in town.

You will get a wide range of answers because every hike and year is different. You have control of much of the expenses except for food.

I can't give any personal insights here as I haven't had to particularly scrimp. But the overall thru-hiker culture is pretty frugal (if not sometimes beyond frugal), and that sort of rubs off. I think even a really rich person who normally lives a carefree spending life would find themselves acting pretty thrifty just because that's the culture everyone finds themselves in — cramming multiple people in a motel room, that sort of thing.

The "start later" suggestion certainly makes sense. I would add the caveat that a good way to keep your food costs down is to start with or perhaps just after "the herd" — so that you can maximally reap what's left in hiker boxes. This is particularly true early on, when folks are typically mailing a lot more food to themselves than they can consume, but to some degree it's true throughout. I hiked with a guy for a while in Oregon who was on a super tight budget, and if he found a well stocked hiker box he would walk out with 8 days of food even if the next resupply option was only 2 – 3 days away. As an aside, one can debate the morality of cleaning out a hiker box because your own budget is arguably insufficient — I don't mean to get into that, other than to suggest that you think through it and feel your way to the best behavior for yourself as you go along.

The thing that's tough for people I think is that you have a great chance of hiking with other people and enjoying their company. It could be very unhappy to see them going into town to zero, shower, relax in a motel room and eat burgers while you grab the cheapest food you can get and hit the trail again. Equally unhappy in a different way is if people come to see you as a leach, trying to sidle into the motel room they paid for at low or no cost or gazing with puppy eyes while they open their resupply boxes from home.

I'm not saying that you can't hike a long trail on the cheap. I do think that for the *average* person it's good to have (in today's dollars) something on the order of $4000 set aside, not counting what you need to get to and from the trail in the first place, nor anything for health insurance or unplanned emergencies of whatever sort. Trying to hike the trail for less than that requires compromises that you really can't grasp, I think, until you have been hiking for a few weeks.

I guess the one saving grace is to realize that it's not the end of the world if you can ultimately hike only part of the trail before you run too short of funds. And that all the thru-hikers around you look, smell, and sometimes even act like hobos too! :-)

When I do long solo travels such as bicycle touring or thru-hiking, I always stick to a budget of $10/day (including unforseen circumstances). For my PCT thru hike I did not see many people after Yosemite and ended up not taking any zeros after Kennedy Meadows and only stayed in one motel at S Lake Tahoe. It is definitely easy to get pulled into towns by others, and that is the only place to spent your money. If you want to spent little money, stay on the trail all the time. Luckily, the trail was exactly where I wanted to be so I even stopped going to towns that were even more than a mile off trail (stopped hitching) and stopped going to restaurants because they really didn't enhance my experience. Just know what your priorities are, and if a top priority is money then know what that entails. To answer your question, I think a frugal 4monthish thru hike can be done for $1000 without compromising the hike. Whether it compromises other things (the nonhiking aspect) is up to your desires. Many hikers seem to spend a lot of their time on trail dreaming about the next town, and if the next town just means going to a grocery and making your pack heavy again, it is easier to experience the trail more deeply.

Some general tips:

Visit hiker boxes before you go to the store to shop for supplies.

Carry the gear to camp comfortably. A few extra ounces for an inflatable pad and enclosed tent will make it much easier to skip a night at a motel.

Seek out AYCE buffets.

Split the cost of motels with other thru-hikers.

Get cash back at store counters rather than racking up ATM fees.

Shop at grocery stores rather than convenience stores when possible, even if it means a longer hitch.

Plan your town visits to head in in the morning and head out in the evening if possible. Skipping the evening in town and the associated motel costs is the easiest way to economize.

Take your zero days on the trail rather than in town when you can. Its very possible to do laundry, wash up, and so on on the trail. You can carry heavy food out of town with you for that first day off on the trail.

Do your research and learn the places that are expensive to shop for food (eg Kennedy Meadows, Vermillion Valley), mail yourself packages from previous stops to these places.

Finally – don't go too nuts on economizing. A thru-hike is a once-in-a-lifetime experience, give yourself enough cushion that you can do it comfortably. Unlike a "real-world" purchase, like say buying a car, where the difference between $13K and $14K isn't really much of a difference at all, a thru-hike is one area where an extra $500-1000 can make a giant impact on the experience. There are people on the AT and PCT every year who have to drop off because they tried to cut things too close and ended up running out of money, and to me this would be devastating. Don't be one of these people.