Maybe check out lightning loop - https://github.com/lightninglabs/loop . Seems much cheaper and is not custodial. They claim 0.05-0.5 %, I just tried quotes for 1M sats and 10M sats, got 0.3% and 0.12% fee respectively. This is service fee, the on-chain fee is not included. Probably a big limitation is that you need to install it and have lnd already running.

Robosats also allows this kind of swap, not just fiat <-> BTC. But their interface is a bit confusing for ligthning-onchain swap, I am never sure whether my offer has premium or discount. And Robosats itself takes 0.2% fee, plus you probably pay premium to the trade partner if you are doing swap out (paying with lightning, receiving on-chain).