Depending upon the exact fault(s) ..................
Expect to pay 1 to 1.5 hrs for a decent diagnosis, and make certain you tell them you want a print out, if they baulk at this, then, well to be blunt they are not doing a proper Diagnosis.
What you do not want is some jackass reading a few codes, and verbally telling you what HE
thinks is wrong, you are paying for Diagnosis, by getting the print out you can come here etc and get second opinions
If it came into my shop, here's how it would roll :-
Car will be put on SDS, get a full Code Read, then a thorough look at Live Data, plus if needed a run with Guided Diagnostic to see what that throws up, then a full Clear Codes and History, then a Test Drive if needed, or run the whatever and try to replicate fault, re Code Read and see what if any has come back.
If it is a simple fault it will very likely get fixed while it's here within your payment of 1 to 1.5 hrs
HTH, Cheers Dave