You could call around to some local repair shops and just ask what they charge to do certain things and base your pricing off of that. If your charging $35 out of your house and there's a local business that only charges $40-50 people may be more likely to trust that the business is going to do a better job for not much more. But if your charging $35 and the business is charging $80-90 people might wonder why you are so cheap. I think I'd try for like 40%-60% of the business rate.
If you really only want to do this part time then stick working for family and friends. But if you want to kick it up a notch don't do personal computer consulting, only consult for businesses. The problem doing jobs for family and friends is they cannot write off your consulting as a business expense (unless they're running a business). Even doing jobs for your boss at home isn't necessarily a good idea for the same reason - it's difficult for them to justify paying say $50.00/hr when it's not a tax write off for them personally.
Don't undercharge for businesses, just be sure to do a great job and know what you're talking about. If you do a great job your reputation will spread. Rely on yourself, not just word of mouth, and be sure to do enough marketing to keep yourself busy (assuming you want to grow). 50-60 clients might seem like a lot when you're first starting out, but if you want to stay in business full time you'll need a lot more or more regular calls (which you probably don't want since it could mean you're not doing a great job). Ask clients if you can leave fliers, business cards, etc. at their place of business.
Unless you're serving friends and family I wouldn't do the $15/hour after the first hour, especially if you have to do any kind of travel (if you're only making people come to your home then maybe). It's great to want to give friends and family a break, but what do you want to do - work for them, or work for yourself? $15/hour isn't going to make you a whole lot, especially if you only do 2 or 3 jobs a week.
Jmacavall has a good point about checking local business prices, but don't sweat it too much if you are higher. If you provide more and/or better service then it doesn't matter that they have a store front. A number of professionals I know don't have an office period and they do very well. For example: one graphic designer friend meets clients at their place of business coffee shops, restaurants, etc. He's always very busy and charges about $1500 for what takes him between 30 minutes to an hour. He's extremely talented, knows the Adobe suite so cold that he's memorized almost every keyboard shortcut, and he keeps a library of his past work on his system to draw on. Computer consulting is different - but you can see having a storefront isn't necessarily a must if you really know what you're doing.
That said it is helpful to have a regular office, even if it's off the side of the house. Not only does it make you look a little bit more professional, but it helps you separate work from home. You'll be less inclined to sit in front of the tube watching sitcoms when you should be drumming up business. Marketing is really important if you want to go far (and part of that is making sure you answer your phone, never ignore clients. You might have to get back to a client, but don't ignore them).
Hope this helps a bit.
