how heavy (max) do you want it to be?
I was gonna ask that. Why don't you get a joiner in to build you a booth. Just build it like a room decoupled room within a room. You might only need one leaf as well, because the other will be provided with the existing walls.
This is my quick plan. I'm unsure the level of isolation which will be achieved, especially for you, but in theory(to me anyway) this should provide one leaf, and your existing wall, the other. Although your existing wall will probably be a stud wall. I'd recommend keeping this at the furthest point of the room from your neighbours. I suspect that this will be similar to the booth you posted, except that it probably is a two leaf(MAM) system.
I left out a window for cost, and you will probably require some sort of ventilation, but on a budget, i doubt this is possible. Just make sure you open the door for a few minutes after every recording. And make sure someone knows you're in there
EDIT: Just read that the booth you linked to(gold series) can be
upgraded to a double wall. So the standard model will probably be not much more than my suggestion(except ventilation and a window). Also, you will need some way of getting the signal out without sound escaping, and power for lighting and amps(if you use it for them).
Want ventilation and a cable port, try and copy these(
vents,
cable port). I'm sure someone here will try to help you out with explanations of how to do this(I would but it's almost 1am, and I'm tired).
EDit: Infact, screw sleep. I'm gonna help you out with the vents(I'll change the pic below).