Best deal for printing OK quality prints from digital photos?

I’d just take them on a thumb drive to your local drug stores and stores like Costco, Office Depot, etc.

Here’s some advice for online services

Costco is really affordable. Just make sure to turn off any auto adjustments. I think they have auto contrast on as a default. The pics turn out too dark.

“… decent print in the mail …

I’ll assume your in the US.  I’m in a similar boat and had good results with Nation’s Photo Lab.  Lot’s of options and I was pleasantly surprised with the pricing and timely delivery.

The cost to upgrade to a pro printer is so minimal I just can’t fathom why anyone would get walmart/costco prints. As a pro, I stopped offering high res files to portrait clients as they print them at costco and look terrible. Seriously, many people say they look “fine” or “good” but if you look at them next to a pro print there’s no comparison. Spend the extra $.10 for a 4×6 or $.50 for an 8×10 and use Nations Photo Lab, or Bay Photo (depending on which side of the country you are on), you won’t regret it.

Oh, and word of advice if you don’t think it’s a really good image: keep prints small they look better that way. That’s why so many photos look great on Instagram… :)