I got my valve cover gaskets on-line for $13/ea. They also have the lower manifold gaskets for $3/ea, but not the uppers.
(Not sure why my 2002 SLK32 has different prices then the SRT-6... so look it up instead)

Auto Parts at AutohausAZ - OEM Auto Parts - Discount Replacement Parts, Resources and Car Care Tips

I found a good German engine gasket RTV at the auto parts store that is in a pressurized applicator can for $15.

I like Rob, Needswings and the ease of everything in a kit, but there are cheaper ways that are just as effective.