have you used legal counsel to review customer contracts? What could be the cost of it? Does $3,000 sound too much? (this is enterprise sale contract for >$100,000)

Yes it does

the cost will totally depend on how much back and forth you have with the customer. We do redlines all the time and $3k is too high unless you are doing something very custom.  I would say our average is between 0.5-3 hours of legal time per review.