I think your main issue will be getting someone who actually wants to do the work - some bodyshops can be awkward about taking on jobs like this! Someone else might know better, but I can't imagine them getting away with only spraying a small section of the door?? Two full doors to be painted, along with the work would cost a pretty penny.
Saw a program on canadian TV at the weeekend that showed you how to do it. Didn't look that difficlut. There's a company that makes ready made blanks which cover the key hole so they just need to be welded in. There's special spring mounted locks you get then too which work off an alarm fob. I'd say you'd be looking at 500 - 750 to get it done 100% right (including getting your doors repainted)