I've recently taken the plunge and done this service myself. I can recommend the following step-by-step set of photographic instructions as a good guide to seeing how it is done.
Step-by-step intstructions
One or two pointers though... be sure you check the exact year of your Reba model against the tech specs on the SRAM website (under 'tech docs for dealers' or something like that). The volumes of oil vary between years, and vary between chambers.
You'll need some 15wt oil and 5 wt oil, plus some other standard tools. Circlip pliers can be had off eBay for £4 delivered. A 24mm socket you should have lying about somewhere? And the only other vaguely specialist thing is a 'soft' mallet made of plastic or wood or something similar. I made do with the wooden handle of a file. Plastic syringes are also invaluable for ensuring you get the EXACT amounts of oil into each chamber.
Tip 1: When tapping the schrader air valve rod off its seal at the bottom of the fork, cover it in something to protect it - I used an old Schrader valve dust cap. Otherwise you could easily damage the valve or the thread. NB. It does require a bit of a bash to get loose.
Tip 2: Ensure ALL the oil is extracted from the damping cartridge chamber, otherwise when you fill it up with the 'correct' amount of oil, it will have too much in, hampering your fork's performance considerably. To do this, push the damping rod up and down while the fork is upside down and the excess oil should squirt out.
Tip 3: Use syringes to precisely fill each chamber with the correct amount of oil. It just won't work well otherwise.
Tip 4: A spot of grease around the fork seals will help them slide back on over the stanchions again.
It sounds like a nightmare, but it isn't - be brave! It's certainly not worth spending £50 letting someone else do it. Basically, if you can build Lego you should be able to service these forks without issues - they're pretty robust! It's worth it once you have them serviced yourself andd they're all running peachy.. 
