The Raiden network, which is a off-chain layer 2 implementation based on ethereum has no transaction costs, see link under transaction fees here. The transaction fees are not a factor in gas cost for a raiden (layer 2) implementation- the real costs of a transaction using the raiden network is the cost of setting up the payment channel - the question is what is the gas cost for setting up a payment channel in Raiden(any estimates or ranges for gas costs while setting up the channels)?
With every contract version bump new gas estimations for all calls are added alongside. For the latest version of contracts (0.10.0), gas estimations can be found here:
If you will have any more technical questions about Raiden, I recommend you check out official developer gitter chat as that is preferred way of communication at the moment:
Hope this helps! :)