Just what in the world do pregnant women wear for special occasions?

As much as I love Target and Old Navy (and trust me, I do), I'm wondering exactly where pregnant women on a budget shop for special occasion dresses? I have half a closet full of "work-appropriate" (business to business-casual wear and suit separates) maternity wear from when I used to occasionally venture out into the real world. The other half is full of sloppy/stretchy jersey maxi skirts, hoodie tie-tops, and pajama-type items that I attempt to pass off as real maternity clothes (most of which were purchased at Old Navy and Target, since their clothes are inexpensive but don't necessarily stand the test of time super-well). This only sometimes works. 
But here's my issue: I'm about to pop and start looking super-huge, which happens for me at 18-20 weeks (I'm already in that chubby, kind of gross, probably would ask if I'm pregnant or ate too many hot dogs phase). I have a wedding to attend in the beginning of July, somewhere in the 22-23 week range. I have to look amazing, spectacular, and breathtaking, obviously. I have only one formal-ish maternity dress that I wore to hubby's award ceremony last pregnancy, but it's won't fit right for when I need it (I won't be as huge-ish at this point as I was for that particular occasion), and it might be a little too casual. So I've been scouring the internets for anything acceptable and in my price range only to come up pathetically empty-handed. So what's a knocked-up broad to do?
My usual go-to places for formal attire are sadly bereft of any maternity-wear. I generally stick with Dress Barn (even though the name sounds awful, they are really great and have a wonderful selection) or eShakti (great, but I'm not ordering something custom for an ever-changing preggers body), and neither of those seem to be options this time around. I've even thought of buying something non-maternity that would fit, like something empire-waisted and flowy, but think that may just look, well, strange and cheapie. 
Stores/sites like Motherhood Maternity, A Pea in the Pod and Isabella Oliver have a great selection of formalwear for all kinds of occasions. The problem? I'm not a zillionaire, and I'm only gonna wear this thing once or maybe twice. Shabby Apple had a few ok options, but nothing really great and they're still a little on the spendy side.
Anyone have any suggestions? I've still got a little time!