I think it could involve another module, such as Content Access (along with the ACL API):

http://drupal.org/project/acl
http://drupal.org/project/content_access

You would then have to write a custom module that hooks into hook_order() - since you are not purchasing a role, but a node - the module would have to allow access by hooking into the ACL and granting access to that node for that user.

Sounds simple in abstract but I haven't done any digging to give you a real concept of the work it would entail. I'm sure it's possible, it just hasn't been done yet AFAIK