Your budget is pretty low for all aluminum. What youll find in that price range is gonna have major cracks and huge plates that were boogered on with a spool gun [a superficial weld at best on 1" thick aluminum] because no one wants to pay for a 500amp tig to actually fix it right.
If youre gonna buy a cheaper cash trailer and fix it yourself go with steel and check real good for rust jacking at the joints before you buy. The weight penalty shouldnt hurt you too often. I have NEVER found the heaviest loads to be the best paying. Quite the contrary.