winterborne are great people and will do an excellent job, but i suggest doing it your self.
after sanding all the old paint off your frame give it a few coats of the colour you desire. i usually do about 2-4 coats, about a bottle and a half of spray paint. make sure you let the paint dry between coats. then get a clear, hard finish to do a final coat or two. if you want you can also start with a primer to insure if you do chip the finishing coat, the steel frame wont show through.
painting bikes your self obviously wont give you the high end results that paying alot of cash will, but it's really fun and gives you a chance to clean your bike, overhaul components while the paint dries, and generally feel more attached to your frame.
i recently did a cruiser red with a black fade at the lugs. i achieved this by holding the black spray paint at a 45 degree angle and lightly going across the bike, then doing the same with the red again and the places the two colours matched. i also taped off some of the lugs and painted them chrome. apparently i did a few too many coats of chrome and it looks all sludgy so ill have to re-do it.