I used a cheap and cheerful place in Mansfield (WH Paints). They stripped (sand-blasted?) and powdercoated a steel frame and fork for £35 for me. I then applied my own graphics and clear rattle-can lacquer over the top, and it’s been great. The finish was superb for the little money I paid, a little thin in a couple of the more fiddly places but good even colour. It’s been very resistant to scratches apart from a few chips on the downtube from stone strikes (the coating is fairly brittle compared with paints). It has started to go a bit “crazy paving” after two years, presumably not coping too well with the heat expansion and flex in my frame?
You’ll need to strip all the components, obviously, and I installed an old sacrificial seatpost, headset cups, BB cups, cage bolts etc to protect the internal threads and surfaces.
If your frame is already powdercoated rather than painted then you ought to look at getting that removed in a chemical dip. It’s possible to do another coat over the top but that might be ugly, as well as heavy.
