Even for very hard to find sizes you can get them for cheaper! I currently wear a 32K/KK and typically spend $40 or less on bras. I typically look at ebay UK, figleaves (they have both a US and a UK website- sign up for their emails and you can get 20-25% off coupons), Large Cup Lingerie- they ship from the UK but the shipping is free and they offer good discounts on sports bras, and Brastop (watch for free international shipping!).
Also, make sure you're in the right size. If you're trying on so many bras I do wonder if you've got the right size to begin with? 80% support of the bra comes from the band so you really want a tight band to get enough support. Check out Butterfly Collection to get a good estimate for your size:
http://www.butterflycollection.ca/bra-size-calculator/ and make sure your bras fit. Signs to check for:
- center gore lays flat against your sternum
- the bra itself doesn't cut into any breast tissue- no quadraboob
- there is no wrinkling in the cups
- the underwires don't pinch and aren't too wide or too narrow
- the back of your bra band does not ride up and its comfortably tight.
- the straps don't dig into your shoulders
ETA: also check out Bratabase:
http://www.bratabase.com/ you can often find good used/new bras on there for sale. Like I PP mentioned, I too buy a lot of Ewa Michalak bras. Those I'm willing to spend a bit more because the quality is so great!