Re: wall treatment
Honey
there are no 'cheap' ways it is all expensive .
I would say the options to curing the lumps and bumps depending on their size are replastering, plaster boarding or papering with a patterned wallpaper .
I had a similar problem in the kitchen and wanting to avoid even more expense (after a leak which resulted in having to have a flat roof replaced ) I painted the area with a few coats of
matt emulsion which does not accentuate the lumps and bumps.