Being in that business I can tell you that Ice said 30-35 is ok. Although going up every 6 months, that I dunno, you have to remember their are places like compusa, which will charge 80 to 90 bucks just to look at the system. So you gotta keep the hourly rate down To attract customers, (and to give them a reason not to goto compusa or other retail places) and to keep it affordable, if you do that, you'll have more and more clients. As far as advertising, you can pin "ads" up at your local grocery store, that "sometimes" works. and is free. The phone book is a great idea, but I dunno how expensive, you can set up a cheap website, through your isp, but thats harder to spread, business cards are nice, And warrenty your work, thats a good, idea, but it was also mentioned earlier that you should always document what you fixed, and what you "touched" so that the user can't come back and say you fixed my modem, now my mouse doesn't work. or something like that. otherwise, I wish you luck in your endeavor...
:cheers