We found a used Nash 27E a year or so ago for around 10k. It has triple bunks stacked in a single column. Our oldest is 7 so it works well. The lowest bunk is on the floor, I could see it being uncomfortable for an older kid.
It's around 29ft bumper to tongue. It's difficult to find reasonably priced bunk house trailer, especially "in" season.
If you are in/around Boise, we got the Nash from Bear's RV in Garden City. The owner is Jeff and he is a nice guy, he sells used units that are priced reasonably. I do not like the pricing of the larger dealers in the area.
Didn't want to go to 32+ft to get a bunk room trailer.