It's the cost of the DHX and MXC tokens as described above, and the (optional) cost of the miner. It all depends on how much you want to earn and can afford.
You can get the costs of the DHX and MXC tokens from various crypto exchanges. To see the list of some of the exchanges that DHX (DataHighway) and MXC tokens are available on, go to coinmarketcap.com or coingecko.com and search for DHX or MXC.