I've done quite a bit of this work. I don't know the condition of your unit and I don't know how good you want it to look when you are finished. I've seen folks spend more on a paint job than they did on their unit. It's often cheaper to buy a unit in the condition you want than buy a cheaper unit and then pay for an expensive paint job.
I'm assuming from the banter that you haven't done this sort of work previously? It's not difficult but it may be expensive if you have to pay someone else to do it.
If your unit is solid with no
fiberglass damage and you just want a color change you may be able to do a lot of the prep yourself.
When I do it I remove all the
windows, moldings and decals. You can mask these items but if you are going for new paint you may as well go the extra mile. It makes the prep easier and new window seals eliminates the potential for
leaks later on plus new decals make the new paint POP!
Next, wash the unit with an automotive detergent (NOT DISH SOAP) and rinse well. Sand with 240 grit all over, no shiny spots. Repair any damage with automotive body filler and sand smooth. Spray with automotive primer. Sand entire unit with a minimum 320 grit sandpaper. Wash off all dust. Examine unit for any small marks that remain such as scratches, pits etc. which can be filled with glazing putty. Sand smooth. You shouldn't be able to see any marks or feel them when you run your hand over any surfaces.
Contact a shop, like MAACO, who will final sand your unit (for adhesion) and apply the paint.
Good luck!