Let's assume I have huge server at home with tons of disks that sucks on average 200W 24/7 - most machines idle around 10-50W depending on the periphials
I'm in Germany, the country with the most expensive electricity prices - I'm paying 31cent/kWh at the moment. That's about the current market price for consumers - so that's 543,48€/year or 45€/month if that machine would suck 200W on average over the year.
If you are lucky have fiber at home - let's say another 50€/month and add 5€ for electricity for fiber and switches and stuff so you pay 100€/month for self-hosting at home.
Using the pricing of the big public clouds like Google, AWS, Azure you can stuff quite a bit of CPU and SSD's and HDD into that machine until you hit the 200W limit.
I just looked at Azure and took the cheapest instances for dev and compared the reserved price for one year (so already discounted)
Azure that gets me a whopping B4s v2 instance with 4 vcores and 16 GiB and no storage and no bandwidth.
Using Hetzner a cheap german dedicated server discounter you can rent a Intel Core i9-13900 with 64GB memory and 2 x 1.92TB SSD for 100€/month.
Realistically you would buy a Beelink SER6 Max Mini-PC, AMD Ryzen 7 7735HS that idles probably around 15W and only pay 40€/year for that. It's 640€ new here and much faster than that Intel machine. You can almost buy two of these and still only pay 105€ a month and in the second year it's only 80€/year.
Of course there is no redudancy, no support, no flexibility your home ISP is probably overbooked and so on and so on - if you just a big machine somehwere that can fail but works most of the time it can be a cheaper alternative.