If you want to do it yourself, a citrus based paint stripper such as CitriStrip is cheap, easy to use and doesn't produce toxic fumes, but it will make a mess (I used it on furniture). The stuff has the consistency of fruit jam and works pretty well. You brush it on, let it sit for an hour, and the paint bubbles and peels off. If you go this route, use gloves and eye protection. Afterwards, you'll need to wipe down the frame and get the stripper out of the nooks and crannies.

Even with chemical strippers, I understand that paintshops need to scratch up metal so that the powder coat will stick. Presumably, since they aren't removing paint they can use a softer media.