For myNode, btcpayserver only available if you use premium version (cost $99) or you bother setup it by yourself.
True. I just now edited my reply to reflect the paid version is needed for the auto install of BTCPay
However, if you are going to be setting up a store, getting hosting, etc. $100 +/- of getting everything going is going to be minor.
You still have to get the hardware for the node anyway or if you are hosting it someplace there is the cost of the extra storage and such.
-Dave