@W3bbo: Unfortunately, you also have to pay an additional licensing fee to upgrade VS2010 itself. So you're talking 10 grand total.
OTOH, VS2010 Pro with MSDN is USD732 for the upgrade price. Each sub includes TFS with 1 CAL. Since CALs can be used to access an unlimited number of TFS deployments, you can install one copy of TFS on a server, and have all clients access the same TFS deployment.
So the total would be USD7320 for 10 devs, even without volume licensing discounts.
It's clear Microsoft really, really wants you to subscribe to MSDN and never let it expire.