So, I'm thinking about having my roof rack rails painted. Can anyone give any advise of how much I should be looking to spend and anything I need to ask or be aware of to make sure it is quality?
I would take them off yourself and paint them. If your unsure on whether or not you'll like it you could use Plasti-dip, which could always be removed later on. If you know you want them black and want the best durability I would look at the spraymaxx brand of paints. They make a black and a clear that are both exceptional quality. It's basically the same as what a paint shop would be mixing and spraying in their guns but it comes in a spray can. You have to activate the two parts within the can and once that's done you have about 24 hours if shelf life. I've painted my motorcycle and used the spraymaxx 2k glamour coat gloss clear for the whole bike. Very easy to spray and great results.
The one time I had something powder-coated (front bumper of a Dakota P/U) I was amazed at how reasonable it was ($75). Of course that was back in the early 2000s, but there's not much work involved for them since you take the parts in and all they do is spray them and put them in the oven with other parts they're coating that day. BTW, the result was outstanding and VERY durable!
Eastwood also has their own brand of 2K paints but I have not used them so I can't speak to how well they work. I painted my motorcycle using duplicolor color paint and finished with the Spraymax 2K clear. The clear went on very smooth and was the nicest spray can I have ever used. It was like using an actual spray gun but with out the mess. The cans cost about $25 per can.
I don't know much about the powder coating process other then it needs to be baked on. My concern with powder coating the side rails would be the temp it has to be baked at if any of the pieces are actually plastic and not metal. I don't have the side rails so I can't say for certain what is metal and what is plastic.
I had mine painted at an automotive paint shop. It's been durable, and when I strapped a paddle board on it, the straps (ratchet) did not scrub the paint off.