The heated grips replace the throttle housing with a new one, hence the 300$ cost. It looks like they are charging you for 2-2 1/2 hours of labor. If you really want the grips, I would schedule it with the break-in service as the bike will already be apart. That may save you money.
I have the heated grips and love them. When its cold this is the only bike I ride. You do have to hold the grip to keep fingers warm, but it definitely works. I also have a desert sled, and I installed the bark busters with their complete covers. It helps but its definitely not a heated grip. I'm a bit of a baby about cold hands though. I've bought about 6 pairs of gloves (non-heated) for the DS and NONE of them kept me warm enough for an all day ride. Heated gloves are a must for me if the grips are not heated on rides longer than 1 hr. Buzz's option sounds great. I have a pair of RST track glove and can attest they are fantastic, premium quality!