Now that you know what's wrong, why not call around to some local shops and get some verbal estimates over the phone? The best information on cost is from local service providers. It doesn't matter if someone 2000 miles away can get it done for $50. It doesn't apply to your situation.
When you get the estimate, tell them you'll call them back shortly with your authorization to proceed. Then make some quick calls to get a ballpark feel if the cost is reasonable. Factor in that the place that did the diagnosis isn't doing it for free so if you decide to pull out and go elsewhere, you may pay a diagnostic fee.