I may regret this, but….

30 degree quilt probably needs 5 oz/yd2 Apex. You'll probably have to wear additional insulation inside.

Quilt is maybe 6 feet x 4.5 feet

so maybe 2 yards of Apex + 4 yards of 1.1

Apex is $16/yd at thru-hiker, 1.1 is $3.20/yd for 2nds at backwoodsdaydreamer

So, $45 total, plus shipping, plus do you need any straps or anything?

If you screw up or decide you want to do over to make it better, then that will add cost

Plus cost of your labor

If you don't consider this an enjoyable experience, if you're just doing it to save money, then it's probably not worth it

I recently made one a couple months ago, Apex 5.0 from thru hiker and ripstop seconds from diygearsupply plus cords, cord locks, Velcro, grosgrain, thread, etc.

All in all, the whole project cost me $75 including shipping. I used the bare minimum of fabric to make the quilt. I bought 3 yards of the 72" wide roll, and cut it in half to get two 54×72 sheets but ended up buying a yard of left over ripstop from local store for cheap to add length since I'd lose some to seams.

Depending on height, you can save money by buying 5 yards of 60" wide ripstop instead of 6, or do what I did with the 72" wide roll. I probably could have gone without adding extra fabric to increase length since I'm only 5'6", but I'm happy with how it turned out.

Another idea to help simplify things a bit, is to buy a cheap, pre-made synthetic double sleeping bag liner and put the apex in there. Some quick hand sewing a bit around the perimeter, or very quick machine sewing wherein you don't have to worry much at all about seams in their various facets. The only part you need to be more careful and meticulous about is the opening end, which is not pre sewn.

I once bought a silk double sleeping bag liner on ebay from Vietnam, and it ended up being a good purchase, and the quality was better than i thought it might be. These same companies also sell synthetic double sleeping bag liners, just make sure the size is large enough before hand. The company i bought from was like Hannatoi, but i'm not sure on the spelling since it's been awhile.