Another option is to think slightly smaller. For $80 you can get the DIY kit for synthetic quilts from
AHE which gives you 8' of either 2.5 oz XP or 6.0 oz high loft Climashield. The 6.0 oz. Climashield comes in a 64" width, last time I checked. That means if you cut the piece in half and turn it sideways, you end up with two pieces that are roughly 64"x48" - more than enough for TWO 3/4 length+ underquilts, and even a single layer of 6 oz Climashield should get you down to decent temps. You may need to supplement the kit with a few miscellaneous items (an extra cordlock or two, some extra grosgrain, etc.) and you'll need to make sure you have a design that works for you in mind, because you won't have any material to waste on experimentation. But with that kit, it's possible to make UQs for two people if you get creative. :)