Good question! In TON, the gas cost of minting an NFT is the same, whether it's the first or the last minting in the series. This is different from Solidity in the EVM world, where the cost can vary depending on the specific implementation.
As for calculating the cost, it will depend on the specific details of your deployment, such as the gas price and the complexity of your smart contract code. You can use the TON Gas Calculator (https://ton.live/gas) to estimate the gas cost for your deployment.