How many miles are on the bike? After 10k miles on my road bike the rear cassette and chain needed replacing (I failed to do proper chain maint or the cassette might have had more life). The front chainring doesn't get used nearly as much and I'm surprised yours needs replacing. The rear cassette had rounded cogs on it :-) The front chainring still looks fine after another 2500 miles. They also replaced a section of cable from the right brifter as it had worn away. They also trued my wheels. I think it was like $250 out the door after the 10% discount. So the quote you have been given does not seem unreasonable. It is not unreasonable to replace pieces of the drive train. I agree with getting another quote.

I see no reason to purchase a new bike, especially if you like the bike you have.