I found a Cleo Maddie in 34GG on Amazon for $24.88. I believe it is good for full on top.

A little bit over your budget, the Cleo Lucy in 34GG on Amazon for $26.80 and free shipping. It's good for full on bottom.

This Tango Classic balconnet in 34GG is 21.90 plus shipping.

The Cleo Lily in 34GG is $26.78. Good for even fullness breasts.

Cleo Millie in 34GG for $26.66 and free shipping.

You might also check the listings on bratabase.com. You can sometimes get bras very cheaply, and the site is also good for reading about how the bras fit shape-wise and comparing measurements of bras you'd like to try to ones already owned. Ebay is another good resource, as andstuff suggested!