... with the possibility of increasing the cap if needed.
I am in the UK and wanted to move to an ISP which offered FTTC, IPv6, a static IP, would be happy for me to run servers and would not implement CG-NAT, and offered good technical support in the event I should need it. The ISP which was most highly recommended to me based on those criteria offered FTTC for a fixed monthly price, with a cap — if paying a proportionate more-than-average-in-the-consumer-market price gave me a proportionate more-than-average-in-the-consumer-market service, that sounded like a good trade-off to me, even with a cap.
Coming from an uncapped connection, I was nervous about buying something with a cap, but, having checked our usage for a three month period, I picked the option with a cap three times that (guessing that a faster connection would mean we use it for me) and, so far, that has worked out well for me. If I want another 100GB, I can pay for that, either as a one-off, on a particularly heavy usage month, or to upgrade the connection permanently.
(The ISP is Andrews and Arnold and, so far, I have been more than happy with them. I guess that they have to pay upstream for capacity, and an unlimited connection would entail a pretty significant premium to ensure that they were not left out of pocket.)