I want to purchase my own modem/router and stop renting from xfinity( already cut the cord on cable service.)
where do I purchase modem /router that is compatible?
what's a reasonable cost?
motorola SURFBOARD SB6141?
This will give you a list of compatible modems: https://mydeviceinfo.xfinity.com/customerinfo
I own an Arris surfboard SB 6141 which you can get for around $50 on amazon, though you'd still need a router (mine is a netgear n600 v1 which you can get for around $50 on amazon). Both of those devices are outdated by now, but still work well enough for my needs (my speed is 150Mbps though realistically I get between 80Mbps and 120Mbps)
If you get a gateway which is a router and modem combined into one product it'll cost more, but you'll have less wires and less clutter since it's only one device. Even if you get a gateway that costs between $100 and $200 on amazon it will pay for itself within a year or two. I've had my router since 2007 and modem since 2013.