isn't there something cheaper, or 120$ is a normal price for a power supply? (my local store)
It is good to invest is very good PSU. This is something that doesn't get obsolete very soon & you can always bring it forward to your next build.
If you are short on budget, I suggest you change your choice of graphics card ($460 AMD7970) and get something more cost effective. The 670 is coming at around $400 or wait for the 7970 price to drop. The savings can be invested into the PSU instead.