This answer really depends on the current gas cost on Ethereum. There are ways to mine "cheaply" though. In the documentation, check out Proof Frequency and Mining Behavior sections.
The TLDR; is if you want to save on Eth cost, you mine with a lower Proof Frequency. This will indicate to the miner to attempt proofs with higher difficulty which results in higher yield per proof and with less ethereum transactions.
RE: Announcing Koinos Whitepaper & KOIN Mining