It depends on the shop. Most good fitting services involve follow up, but I agree that they can be expensive. I'm mostly suggesting you could be quickly served by a reasonable, sanity-based fit as a starting point. Also your pedaling position should be mostly similar for mountain bikes and road bikes.
30 degree bend of the knee feels pretty extended. Basically if your saddle is too high you won't be able to spin as smoothly and your hips will begin to rock and cause lower back pain. If your saddle is too low your power output will be lower and it can cause knee pain.