For a one-time shot, it's probably not worth it. It should take your LBS mechanic only a few minutes to complete the job even if he works slowly. However, the tools are pretty cheap. I just checked Nashbar and you can get the two tools shipped for probably under $20. Maybe you could watch while the job is done and then decide whether you want to spring for tools for when you want to change ratios, upgrade to Dura Ace, replace worn-out cassettes, etc.
-soma5