This is probably a stupid question but is there a way to obtain Plesk licenses for VPSs in the same way you buy cPanel or DirectAdmin licenses for $9-15/mo? The Parallels site has some leasing options, the lowest of which is $40/mo but I assume that is only for one server/VPS. Do Plesk resellers exist?

Parallels partners can't resell to outside facilities the way that some cPanel resellers do, but yes providers do resell Plesk licenses. Here are all your options for resellers:

http://www.parallels.com/partners/find/sp/