I’ll second Triple-S. Used them twice now and have no hesitation in using them again if needed. Relatively cheap (can get frames done a LOT cheaper but you definitely get what you pay for) and they’ll mask off all bearing/bottom bracket/headsets surfaces etc.
My Blur 4X was about £100 from Triple-S incl dipping. They specialise in old motorbike stuff etc so know how to treat stuff (ie, they’re not going to go blasting your thin walled steel frame with ball bearings to remove the paint!).
If you want cheap and semi decent, theres a place near the station in Sowerby Bridge who did a frame and forks (incl. stripping) for £35. Wasn’t the best job but for £35 is was good. Didn’t need it to be perfect as it was only an old hack.
Just don’t use Specialised Coatings (???) in Halifax. They’re more used to coating things like fire-escapes and it showed when they did my old Soul. Had powder in every surface and an orange peel effect.