Track rental can be complicated ... requires insurance, up-front rental fees and an organizer who's willing to accept the task. It may be easier to team-up with an organization who more normally does track days, or DE's (driver education events) like BMWCCA or PCA and request that a CLK (Mercedes) only run group be accepted. As for costs, it can range widely from under $200 to over $300 depending on how many people it takes to break-even as most car clubs don't view this as a money making venture but as an event for their members ... who will always come first, a dilema when trying to insert others.
There are tracks - Carolina Motorsports Park as example - that are able to be more cooperative and accommodate smaller groups and still be affordable. If there is sufficient interest, I will provide a contact at CMP.