Is there any service like Travis CI or CircleDI that lets you add your own slaves? Jenkins let's you turn a box into a slave by running a simple jar file.

It would be nice if CircleCI or Travis CI offered as that would mean not having to pay them for instances and instead turning AWS instances into CircleCI/Travis slaves at a lower per-instance cost. I'd still be happy to pay for their website and for their system managing the slaves.