I agree that servicing regulators is not rocket science, but we are talking about life support equipment. And what happens when you run into the unusual problem? At depth?
Not all dive shops charge too much, especially if youve maintained the warranties.
Best bet is to get affiliated with an authorized dealer who sells your brand(s). They can get the proper service kits, training, service instructions, etc. And they usually have experienced techs for those cases of nasty surprises. Also, manufacturers are hesitant to sell to just anyone, so you might otherwise have trouble getting kits that dont have old, oxidizing o-rings, or parts that have since been recalled, or even a kit that really matches your model reg.
BUT, if you absolutely insist on going out on your own limb, then consider Vance Harlows book
SCUBA Regulator Maintenance and Repair . IMO its not as good as Pete Wolfingers
SCUBA Regulator Savvy , but Vance has some suggestions for the non-affiliated repair person. I prefer Petes book because it really helped me understand the internal workings of these things better than I ever had before (more theory). Or read both . . .