The trailer in our sig is kind of unique in that it has three stacked bunks. It still has a wide slide for the dinette and sofa, so we have plenty of room, and we don't have to convert the sofa or dinette for sleeping. It's worked very well for us. We have three teenagers, twin boys that are 14 (5' 9" 160 lbs, and 5' 6" 170 lbs), and our daughter is 17 (5' 4" 135 lbs). The bunks certainly aren't roomy, but the kids didn't complain, and slept well. My trailer is a 2010, and used ones should be in your price range.
We're borrowing a friend's rear bunhouse trailer for our vacation this year, a Springdale that has the rear bunk room with three bunks, two on one side, and one on the other above the outside kitchen. It's also newer.