Could relays be free and paid at the same time? Accept notes of a certain size freely but come back asking for payment of LN invoice to accept notes containing more data than their set threshold?
Discussion
It's possible, but data storage is the cheapest part of hosting a relay. The actual instance (compute) is usually the most expensive part. If right size everything and leverage Docker containers can keep costs down for a very robust network like we have. Of course the more data the more processing so have to take into account.