There is a view that you don't need a full chamber, and that those little boothettes that wrap around the mic are just as good.
This is probably true. You can even make a home made one, using padding in a cut down box. Hanging up duvets is cheap and non permenant.
You know I'm an esmono man for drums, but I bought a second one for my dining room, so I could sing badly in private. A gaggle of pensioner neighbours
would sit just over the fence outside my dining room. It was all about privacy. I can try to find something good about my singing, without the humiliation.
Booths do several things:
They keep noise in. You can play whenever you like.
They keep noise out. (vehicles,children playing, bird song, strimmers, the wind, etc)
They control reflections.
A DIY solutiuon will probably only do the latter.