Rachel - having been in the dental game about 12 years now, if you have any questions fire away.
An endodontist (root canal specialist) is trained in doing all the tough root canals, they arent easy to do, the hardest thing dentally to do, much easier to pull it out (from the dentist POV). They ae the only way to save the ooth though and if your dentist is referring him then you should thenk them coz otherwise they could have told him they did it and just waited for the infection etc to set in. Atleat this way he will get it looked at properly.
On the dollar amount, it varys depending on how many nerve canals there are in the tooth, they can quote over the phone coa they would havea standard price for molars, incisors etc and a molar GENERALLY has 3 canals. I have myself had to get RCT done by an endo and it cost me $1500 which was mates rates!! Their equipment etc is very expensive unfortunately, its like the words preganacy and wedding, as soon as the word dental is used the price jumps up 100%!
Please let me know if i can help out at all! If you have copis of xrays or anything i am happy to have a look if you can scan them etc.