The drivetrain on my bike needs replacement, given the cost, do I just get a new bike?
I think the appropriate question is not what you paid for the bike, but what it will cost you to replace it. Almost any bike can be repaired (although the grandfathers axe problem also occurs).

I think it's worth doing the quotations yourself. Go over the bike properly and work out which parts need to be replaced, what tools (if any) you will need to buy, and what that will all cost. Then look at the cost of a working second hand or new bike. One advantage of the new(er) bike is that it doesn't have to be the same as your existing bike - if you've been wanting a bigger frame or something the new(er) bike can have that. Of course, a second hand bike will probably also need bits fixed up, which is something to add to the cost.

My expectation is that unless your current bike was fairly good to start with that a new bike will work out cheaper. But if you enjoy working on your bike you should count some of the cost as entertainment (I am building a four poster bed and selling it to my partner this way :)