time is an estimate if all goes perfect I suspect
I suspect the hour and a half is an estimate for onsite time if all goes perfect and most people tend to underestimate time.
One thing here is that the table mechanic is taking over a job somebody else started. I haven't done tables for others but I have owned auto body and mechanic shops. My stock answer when someone asked me what it would cost to finish a job the customer had started was that it would be more than if I did the whole job myself. Occasionally true, more often I ate a little extra aggravation and charged my normal price. Very rarely did I charge less because I had to come behind someone else!
Any table mechanic with the experience to do your table right has came behind enough other people's messes that he is never going to quote you a lower price to take over a job already started sight unseen. If he sees a real time saving from what was already done he might discount a little if he is a nice guy. However another post is absolutely right, you are probably looking at two hours time spent offsite and driving to the job to get it done besides the "hour and a half" onsite. Business expenses too of course. The $350 includes all of this and unless he has to do significant unexpected work he will probably stick with that price if he actually spends two or three hours setting up your table. If he does charge more he should tell you what it will be as soon as he looks over the job and checks levels.
No decent mechanic is going to slap cloth on the table and go from there without checking that everything else is right. His name goes on the job just like mine was when I took over from other people. He has to be sure the entire job is done to the level of any of his jobs which may mean redoing the entire job.
$350 might be high for someone putting cloth on a table or very cheap for someone that does a half a day's work with the tools to do it right. Glen is a bit into toys and overkill but I recall a picture of his where it looked like he had over five thousand dollars worth of precision levels on a table. $350 isn't out of line if you get a quality job.
Hu