Okay I am kinda in the same boat right now, so I'm glad you posted this. First, the price you were quoted is actually pretty good. It's a lot but not as much as I will have to pay. All in all I will have to pay over 1500 so if I could get it done for 740, I probably would.
Second, what others are saying about teeth shifting is very true. Back when I had braces, the first time, they pulled two teeth up top. It was customary then, I don't think it is now. Anyway I've had braces two other times since b/c those spaces keep opening back up. I was told that I probably had enough room to shift my teeth without removing those teeth and now it's too much room. Now I am very picky about my smile, most people probably would not have gotten braces again as the spaces were not huge. I just didn't like it.
Now my daughter is missing one of her molars, it just not there. As a result, the tooth above it came to far down. Now it has never caused any problems, but she is only 15. I say that to say your tooth shifting may not be that big of a deal. I am not a professional, so I really don't know.
A friend of mine had a tooth removed years ago in lieu of the root canal and hasn't had any problems since. She was about 20-21 when she had that done and we are 34 now. Not that old so I don't know if she will in the future. I'm sure it varies from person to person.
I do know that I am not sure what I am going to do :P The other comments help some and scared me a little. I wasn't even told the tooth was infected, he just said you need a root canal. It caught me by surprise b/c 6 months prior at my cleaning there was no mention of a cavity or me needing a root canal.
Not sure if any of this helped, but good luck!