I'm in basically the same boat as you, I've been diving in the waters off of New England for the past four years in a 7 mil wetsuit. This fall I'm looking to get into a drysuit, so I can extend my diving season and be a little warmer. I don't have a whole lot of money to throw at such an exspense. I've looked all around the web at different dry suits, and tried a few at demo days. I think I'm probaly going to buy the henderson arctic 2 drysuit. It won a RSD best buy and a testers choice award. I found it at my LDS for 500, which includes the drysuit course. One of the many things I like about this suit is that all the options come standard, such as kevlar kneepads and molded boots. I've been told that this suit is quite warm and that you only have to wear a polyprop. base layer to wick away moisture. It seems like a pretty good deal to me.
Hope this helps