An idea I've thought about but abandoned personally: Getting market prices/reviews for services (contrasted with goods. That is, the prices charged by plumbers, auto mechanics, etc.) It's easy to find out the going rate on a 1 TB external hard drive. Not so much regarding replacing brake pads in a given zip code radius.
As a sweeping generalisation, I find people of our generation (assuming we're all young twentysomething hackers, mostly) far less informed on what you should be paying for these sorts of services than our parents. Of course, it doesn't help that a lot of us are happy to throw money at the problem as long as the prices aren't too unreasonable.
You know, talk about replacing brake pads! I just had mine replaced, and I had this coupon that made it $99 for resurfacing and other labor (of course the replacement was another $105) instead of $159, so that worked out well. If you're actually interested in that sort of thing, I highly recommend actually opening that ValPak junk mail, there's usually some really good coupons in there.
Not a weekend startup, of course.