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.