Was that quote based on them doing
all the work, prep, shoot, polish, etc? Would they be removing the parts to be painted? $400 for a good professional job sounds reasonable. That's a tenth of what a medium-to-high grade job costs for a car.
All the painting websites/info/etc apply to motorcycles the same as cars. You can certainly learn to do a decent job yourself but it would be an exercise and you would need to invest in the proper tools.
The part that takes the most specialized equipment and controlled conditions is the shoot.
I'll bet that if you remove the pieces yourself, do the initial prep and then do the wetsand and
final polish you can get a painter to do just the shoot for much less.
PC.