A guy I work with and I both went through this last summer. We have essentially identical 1980's Specialized Hardrock rigid steel MTB's. He took his to the LBS. Cost him $200 for a whole new drivetrain and brake cables. They replaced with identical low-end stuff (such as rivetted chainrings).
I converted mine to SS myself. It cost me about $250 (not counting the tools I bought). I lost 17 gears and spent greater than $50 more than my friend. On the other hand, I got the bike I wanted with nicer quality components. More than that, though, I got to do the work myself. That's why I did it. I just wanted to do it myself.