It's important to have an answer to that question, rather than to assume that being offline when your home internet is down is inherently a problem. You can safely estimate using "X nines will cost X digits per month":
1 nines, 36.5 days/year downtime is $#/month. (openwifi tier)
2 nines, 3.65 days/year downtime is $##/month. (residential tier)
3 nines, 9 hours/year downtime; are $###/month. (commercial tier, datacenter tier)
4 nines, 1 hour/year downtime, is $####/month. (datacenter tier)
5 nines, 5 minutes/year downtime, is $#####/month. (carrier tier)
Speaking from experience, it's both important to decide which 'nines' you require before you invest in making things more resilient — and it's important to be able to say things to yourself like, for example, "I don't care if it's down 4 days per year, so I won't spend more than $##/month on hosting it".
https://www.init7.net/en/internet/fiber7/
they explicitly (used to?) market that they don't throttle but simply connect at line-speed "because we can"
Though the small cost is probably overshadowed by the large infra costs at home. So now you need a 25Gbp/s router, together with the rest of topology like qsfp+ switches, and then actually computers with >= 25Gb/s nics to make use of it. And then all the appropriate cooling for it. It’s starting to sound a lot like a home data center :P
https://en.wikipedia.org/wiki/Bell_System
https://en.wikipedia.org/wiki/Xfinity
https://en.wikipedia.org/wiki/Verizon
etc.
Regular 1Gb/1Gb is around 40CHF/40EUR often.
The way we sliced up space for utilities (lots of legal shared monopolies/guided capitalism) and their desire to build the last mile in their area leads to many different prices and products within a walkable distance. Before that 500/30 service showed up the best we had was unreliable 200/15 from another provider.