Documentation on Gas Cost/Fees?

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The 0x Launch Kit sets up a forwarding contract which converts ETH to wETH and then does the 0x transaction. It seems there are two costs associated with this:

1. The gas fees of the ETH to wETH transaction.
2. The protocol fee of the swap (gas fee + protocol fee).
3. The gas fee of the assets switching wETH to ETH again.
4. The gas fee of returning the users transaction.

(Perhaps these are bundled in single transactions but, thats still all the fees.)

In the launch kit, we're asked to set a Maker/Taker fee, but it isn't very clear what costs we would expect to cover from those fees.

In the documentation we see that the protocol fee is "tx.gasprice * protocolFeeMultiplier" and that protocolFeeMultiplier is suggested to be roughly equal to 150000. But, it isn't clear what we should expect for the average tx.gasprice - and while that is the protocol fee from the 0x documentation, it doesn't note what we would expect in costs from the forwarder contract.

Any insights here?