Diamondbacks msrp is $200 on that bike. See if you can talk them down.
Is it a 05' or 06'? 05's were actually more expensive and nicer bikes. I have two 06's sitting on the floor at our shop. They are a decent beginner bike, but expect it to ride like a $200 bike. The shift components are ok, but the fork is the weak spot of the whole bike, it is kinda cheazy.
Note if the stem is 1" theaded or 1 1/8" threadless. If its the 06' it will have a threaded stem, and it will be hard to find a decent fork for it since most high end forks are 1 1/8'