I'm going through this right now.
Auto paint is very expensive!
A pint can cost $70-$120 plus reducer for about another $20. Then you have the clearcoat which runs almost the same. Then you have Evercoat Lightweight Filler which was about another $20. Oh, don't forget a good sprayable primer/filler for another $15.
At the cheap end you might get by with $100 or so if you can use the aerosols. The opposite end maybe $250. I'm not counting anything like a spray gun or sandpaper. I've got a Sata MiniJet gun (about $350) and compressor so I'm good there.
Problem is the color match. You cannot get a good spot touch-up and make it blend well. Even playing with an airbrush to blend isn't easy. You'll need to do the whole panel. BMW metallics are very hard to match, especially silver varieties where the "flop" (i.e. color-shift viewed from various angles) comes into play. - it makes touch-ups stand out pretty bad. I've had two different mixes made (pints at $75 ea.). First was terrible (too dark). Second was better, but still will require a complete spray to make it appear normal.
You can just purchase the lid portion of the case (painted) for $380 if you shop around (Hammersley or Chicago). Hammersley seems far quicker on orders (less than 2 weeks) doing it online.
Depends on how much you want to spend and if you feel the DIY route is the way to go.
Myself, I've given up trying to blend the Crystal Gray
color. It's a bitch!
Dupont says that silver is the most popular color of all out vehicles there, but also the hardest to match (which may account for the popularity?). I ended up buying all the panels from Hammesley and will spray the old ones once they're off the bike. Maybe a new color scheme once I drop it on the left side and get a panel for that side.