I think aluminum is out if you want to stay light
. I think your original price point is doable with patience and persistence. Fiberglass rvs vary in price by location so what's pricey over there might be cheap near by. Try this site Molded Fiberglass Trailers | Fiberglass RV's For Sale
and check Craigs list a couple times a day. When the deal comes along it won't last so be ready to act. In the document centre of this forum you'll find a buyers check list. I searched for months but finally picked up a 13" Boler
that was ready to use for $3000. I was purchasing it 3 hours after it was posted.
Best of luck on your purchase and future adventures.