It would cost in the region of $1500 (750 quid) to refurb a tank in NZ, that’s assuming its not TOO bad. The process varies but usually the bottom is removed to get at large dents, I’ve heard a coarse sanding wheel is used to grind the weld/edge off, as very little metal needs to be removed. It’s either tig or gas welded back on and pressure tested.
A reputable chrome plating company is needed of course, I’ve no personal experience of using one for a tank, there is one well known plater in NZ who most people use for the bigger jobs, maybe someone can give some tips on the processes needed to get a good result eg base layers etc.
As someone else said, the tank ends up thinner due to the heavy polishing needed on the bare steel (usually done by the plater) so it will be more prone to dents even tho it cost a fortune to refurb. That’s why some go for new Indian made tanks.
Painting is also expensive as it involves quite a few hours of work, the only “special” part is preparing the chrome to be painted over (and getting the shape of that area right) I used fine wire wool and then sprayed my B31 tank myself using an airbrush bought just for that job (sticky tape pin stripes), but any experienced painter should know what to do.