I had about the same needs and looked at doing the self build. I ended up with a Work & Play 18LT for only 50% more dollars than your budget.
It was a easy deal, got ready to do Moab in a couple of weeks after buying. Used it for a number of trips, and it worked great. Much better build quality than most of the rv style toyhaulers. Those are just stick walls on frame, with usually rubber roofs. The Work & Play are solid walls, and bolted on all 4 joints, and seem to last for years. They are heavier, and the longer ones are the same price as the 16' and 18' when I was shopping used. If I had been looking for a bigger W&P I could have traded up, as those were wanting to trade down, due to having too small of tow vehicles.
Good luck with your build.
Pantego (DFW) TX
1998 Foretravel 36' Unicoach 295
Just sold the 08 GSA Adventure