What to do when a contractor pulls a huge number out of the hat after the fact?

[Joe S.]

 So we got a call from our property manager and said that the toilets were backing up.  She sent a reputable plumbing company out and they gave us a $9000 bid to do excavating, repairs, etc. due to some roots getting in some plumbing under the house. We thought that was a bit high.
My wife talked to a plumber we had used on a couple of jobs in the past that was reasonable. He went out there and told her that he would take care of it and the price would be reasonable. She said how much and he said he wouldn’t know until he got started. Whereas we have used him before on stuff we were thinking he would be well below the other bid.. Now after the fact, he sends us a bill that basically outlines taking care of all the same things the other bit mentioned, but he is  wanting 23K after the fact.  Obviously, we never would have used him if we would have known he would’ve pulled a stunt like that. We did not agree to pay him that much and feel like he took advantage of us not getting the firm price on the front end. We are not sure how to handle this, but I’m considering talking to counsel as far as an attorney goes. My wife sent him the original bid of the other plumber and he has not got back with us yet. I think this is extreme price gouging, especially since we did not agree to pay that kind of money and if he was expecting that kind of money, he should not have awaited to the very end to tell us.  Basically he’s burning the bridge down for all future work that we can do together as well.

I believe in paying our contractors and I’ve never had an issue in 20 plus years. I’m not an upstart investor looking to shaft somebody. At this point in time unless he comes way down off of his invoice I don’t see any way around this getting ugly.  Has anyone dealt with something like this before?