I sprayed mine flat black with rattle cans, but I'm pretty sure the product I used has a range of colors. It's called VHT flame proof paint and good to 2000F I did the whole exhaust system, the mufflers don't need as high a temp paint as the headers.
VHT has pretty cryptic instructions, and there's not a whole lot of help on the web. Their primer is also poorly labeled; it's in the same can as the paint (doesn't say primer on the front) so you have to check the color code on the back near the bar code. About $10 a can. One of each should handle the mufflers.
There are other high temp paints out there. I think POR makes one
Then there's the cost of prep materials. I used sandpaper in some spots, but some would say that they should only be blasted or chemically cleaned. Don't skimp on the prep, it's the most important part of a quality job. Monte just put up a good post in a thread about painting fairings. Your mufflers aren't fiberglass, but a lot of the principles carry through.
For more money--you'd have to call around on prices--you could have them chromed or powdercoated, though not all powdercoat finishes are suitable for exhaust.
For a whole lot less money you could try oil blackening--think cast iron pan--but I'm not sure how that would hold up to the elements.
