I’m using cards from www.digital-devices.eu; a Cine S2 v6.5 from 2015 and a DuoFlex S2 v4 from 2017 for 4 DVB-S2 tuners total. I’ve found them to be of high quality and the upstream kernel supports them.
Unfortunately, it seems the modular hardware I’m using is no longer sold. The cheapest currently available product is an expensive 8 tuner card.