You could get a bog standard NAS with Time Capsule functionality and have it backup to that. It's a bit more involved setting it up, than an Apple Time Capsule. But it's an option. Works well with Synology NAS's. Though I don't backup to my own as I have a Time Capsule I bought before the NAS (the NAS is where I store all my music, images and videos, the Time Capsule is just for backing up the machines since my music, images and videos easily clogged up my HDDs and Time Capsule).
http://www.synology.com/en-us/support/tutorials/481
Is there nothing I could run on a Windows machine that would act as a Timecapsule service?
No chance i am buying another bit of hardware
