if it's just a rocker box gasket it's an incredibly easy fix, maybe a couple hours time. you'd maybe spend $50 including beer (in my case Gin) if you already have the tools to do it. That's a damn good deal. The lower rocker gasket and upper gaskets I think run you around 25. I'd personally rotate my engine to change them, we have a walkthrough of how to do that. It's pretty much the same on all xb models, the newer ones have less wiring to worry about though.
Where are you located?