What is your parameter to determine the initial price of this coin I don't see any kind of token sale or ICO for this. This is the fork of the BTC blockchain and people will get airdrop so nobody can set the starting price for this coin?
One approach is to look at the Bitfinex pricing last year. Bitfinex traded a pre-launch token for BTG between the October 24th fork date and the November 12th launch date. (Technically, there was no airdrop - BTG was created by taking a full copy of the Bitcoin blockchain on October 24, so all pre-fork balances come directly from the Bitcoin balances at that time. The BTG ledger goes back to 2009.)
Anyway, since Bitfinex allocated tokens directly to all Bitcoin holders at the time of the fork, and opened a market for them to be traded immediately (and those tokens converted to live BTG at launch), you can see their trading price history - which was generally between $100 and $160. There was a brief spike just before the actual BTG blockchain launch on November 12th, and then trading returned in the $150 to $160 range. This is probably a fair assessment of where BTG "opened".
Here's a picture from Bitfinex for the relevant time period: