I took off the splashguard today and saw a black tank on the passenger side near the fog light that looks like part of the A/C system. It's rusting on the bottom and looks like it's leaking, what does it do, how much to replace? Thanks.

 

It is called an Accumilator. It removes moisture from within the A/C system.
It should cost about 1 hour labor plus part. Not sure about price of part. But should be below $100.00.

 

Thanks, when I saw it was part of the A/C system I got really nervous, now I'll be able to sleep tonight.