A new #22 head will be $2000 list, $1600 wholesale, and comes bare (no valves, etc).
Used heads are typically $800-$1200, sometimes they include other stuff you may or may not need (valves, lifters, prechambers, cam, etc). If you buy used, ONLY get casting #17 or higher.
OE rings are about $600/set, aftermarket are cheaper, but I wouldn't mess with the bottom end if it was running OK prior to ths. The 603 has a pretty long-lived bottom end.
The OE/dealer gasket set when I did this job a few years ago was an Elring, btw. Photos of the whole process are here:
http://www.w124performance.com/images/OM603_head_replacement/
