When there is enough supply in a few months, the ZEC price will reduce to between 0.1 to 1 bitcoin.
A bit optimistic? It's in that range now and there'll be around 100 times more coins in a few months.
True value is determined through cost of mining. I have a 10 Sol/s contract for 4 months with
www.Zcash-Miner.com which costs me 0.125 BTC. I am mining since Genesis block and mined 0.01047092 ZEC so far. So, true value of 1 ZEC right now should be 0.125/0.01047092, i.e. 11.93782399 BTC. As more coins are mined, true value is expected to go down and settle at 1 BTC. Whatever value is shown right now on various exchanges are result of trading.
Your calculation needs to be prorated. It is pointless in any case, as market value determines the cost of mining not the reverse.