Users of tbtc v1 pay a signing fee of 0.05%. On a 1 btc deposit this represents a fee of ~$20, and ~$100 on a 5 btc deposit. The ETH fees for minting at current (~30gwei) gas prices are ~$300 - $500.
Node operators currently receive signer fees + KEEP network incentives. The network incentives are slated to stop at the end of November, at which point signing fees will need to be sufficient in order to convince node operators to continue providing collateral for tbtc v1.
Right now there is rarely 5 or 1 btc minting capacity, and tbtc trades at a 3.6% premium over renbtc and wbtc on dexes. This implies that there would be plenty of demand even with higher minting fees.
Therefore, I propose we start to slowly increase minting fees over the next few months, and use a 1% fee as a starting point for our discussions.