It would be great if you would offer simple buyout options.
During checkout or as a purchase upgrade for users that already have servers to pay an extra monthly fee for 12 months or 24 months for high end servers in which the user now fully owns the server.
Once the user owns the server they can continue under co-location costs.
Doing this can generate a client base that sticks with you, allows them to lower their costs after the buyout duration which in turn may enable them to get another server.
There are lots of positives in doing this.
Right now I do this with another provider and at the end of the terms they just move "my" server into their co-location my monthly fees drop and after about two months I pick up another server, keeps them from having to many used servers around and it keeps me growing and stable.