If you're in North America, Newegg has good prices on the parts.
That's assuming you're willing to assemble the system yourself.
There are a lot of tutorials/videos on how to, and it isn't that hard of a process.

If you're not happy assembling it yourself, I'd go with a friend; you can buy beer or pizza.

A computer store will probably charge you a couple of hundred for the service.
But if you want a warranty through the store, rather then the manufacturer warranty that is a consideration.
Again shop around..
One store near me, will do the manufacturer replacement process for you.
Another has an "instant product replacement" program, where you get the new part immediately.