Find a floral knee length day dress for me for about $35 bucks tops? ?

It will be worn to an opera. I was thinking of wearing such a dress with my brown cowboy boots that go halfway up my calves. It will be worn the whole day sightseeing so must be casual. It's not a fancy opera, but a "casual dressy" look. I am overweight. No thin straps, I don't want to be pulling them up all day. Thank you! -try kohls or jcpenny?