Belk also has a lot of dresses on sale, and Nordstrom even has some decent prices on their sales dresses.
OP, If this is the school I think it is, Lilly Pulitzer is quite popular. You might find a Lilly dress in your size at Plato's Closet, or another upscale consignment shop.
Something like this would work for 2nd round with a pair of cute, flat sandals:
http://www.lillypulitzer.com/product...te+Chum+Bucket. I am not suggesting that you get that identical dress, just keep that style in mind when shopping for dresses.
or this:
http://www.lillypulitzer.com/product...een+Hey+Sailor
DDDLady's dress would be good too.
This is similar to one of your choices. It is on sale from Belk:
http://www.belk.com/AST/Main/Belk_Pr...dropName=Women