Here's a step-by-step:
http://www.pedrosgarage.com/Site_3/Change_Spark_Plugs_%26_Tubes.html
I'm no mechanical genius and I was able to replace the plugs, tubes and gaskets in about 1-1.5 hrs, as I recall. Really a very easy project with basic tools. Plugs were ~$60 total and a set of tubes and inner/outer rings were about $50-$60 total.
Don't be intimidated. You CAN do it yourself if you want to take a little time to learn. As you can see from the link above, this job is totally unrelated to the valve covers.
The dealer is trying to totally screw you. (That's why they call them "stealers.") Their mechanic can probably knock the job out in 45 mins. :-) Seriously, dealers or indy mechanics have their place; I leave the really hard jobs for the pros.
Also, get yourself a Bentley shop manual. It's invaluable. The best $65 you'll ever spend.
Where in NJ are you located?