Impossible to get reliable data without the cooperation of local vendors. Local businesses are extremely difficult to sell to. From personal experience, I can tell you that the time-cost of acquiring each vendor is 20+ hours, and the value is nearly zero (since you need thousands of vendors to make the product work).
That's why successful directories of local data (Yelp, for example) use crowd-sourced data.
As far as your issues with your mechanic: check out YourMechanic and RepairPal. Also read about RedBeacon (which has now pivoted), TaskRabbit, and Thumbtack. Yelp is also now using their influence to bring business on-board to give quotes via Yelp as a platform.