In Chicago we have many different organizations that provide special interest classes in like yoga, fencing, baking and people are charged like $45/class (1-3 hrs)
I'm not a mechanic, but you may want to consider hosting targeted cycling classes. For example, beginners: repairing a flat, lubing/cleaning the chain, adjusting the seat...for an hour, I think people would pay $15...if you include a patch kit or some kind of product with your ad on it...may be a nice touch. Moderates, wheel/spoke adjustment/replacement, derailer basics, rider geometry...this is more complicated and may take business away so $20/hr for a 1 hr class--toss in a cheep spoke wrench. And "advanced", the basics of a build: bottom bracket, cranks, cogs/ratio, chain line...This is more problem centered and would require more of your time, so $25/hr...toss in a cycleing cap with your ad on it. Also, work out a structure to work with a person to build a bike themselves...same price ($25/hr and supervise their work in your shop; use your tools and make sure they don't loose a finger...)
word of mouth will boost business and
I suppose more foot traffic through a store would increase
promote it at schools/universities, cafes, parks etc...pick a day a week (sunday) in the am then pm.
I am tossing out fees based on what a reasonable person may pay...that being said, I probably would have paid that much for each. If you/ your staff have a nice personality that will create even more loyal customers...
Great idea...good luck! Oh, mind the sun.