I painted my stock pipes black some time ago. Here's the thread:
http://www.motorcycle-journal.com/fo...ock-pipes.html
I sanded by hand using emory cloth: 60 grit, 100 grit, 150 grit. The paint filled in the sanding and left no visible marks at all. Since it was an exhaust, I obviously was using high-heat paint, in this case Rustoleum BBQ Black. So far I've only had to do one touch up on a small spot where someone put the boot to the pipe and melted a bit. When I scraped off the melted stuff, a small speck of paint came with it. Touched up beautifully, though. Not noticeable at all. For that reason, I would also advise not doing a clear coat. The beauty of the rattle can job is that you can touch up the mistakes.
In case anyone is wondering, I priced a sandblast/powder coat job on the stock pipes at around $200. I also called around a few body shops and found an auto painter who said he would sandblast and paint them for $100, but I would need to supply the paint, since he didn't stock high-heat paint.
Since you're looking to do crash bars and don't need high-heat stuff, I bet you can find an auto guy to paint them on the cheap, if you don't want to put so much elbow grease into it. I just figured I would do it myself first, since I would only be out $5 for emory cloth, $5 for spray paint, and $5 for prep solution. If it didn't last or looked like you-know-what, I could always take it to a pro to sandblast off my mistakes and do it right.