The rent would be for a 3-12 month contract, your call. I'm thinking a price of about $150 a month. I pay cheap prices for electricty and you are taking on the risk paying upfront, so it seems fair to me.
Your $150 per month rate would be appropriate now, however as difficulty increases it will become less and less appropriate.
Would you be willing to consider any longer term leases when the price per month declines each additional month by an agreed upon amount?