> For a small sauna, basic wiring may cost around £100 to £200
4.5kW @ 230V is 19.6 amp, while it seems the British outlet maxes out at 13 amp, like the following quote from https://www.plugsocketmuseum.nl/British1.html :
> BS 1363 plugs are required to carry a BS 1362 cartridge fuse. Existing BS 1362 fuse ratings are: 13, 10, 7, 5, 3, 2 and 1A ampere.
The same site says British ring circuits can typically handle 32 amp (see https://www.plugsocketmuseum.nl/RadialRingCircuit.html ), or 7 kW, so I assume the "basic wiring" cost is to wire into one of those existing circuits.
Which isn't something a renter can likely get away with.
In the US, 4.5kW @ 110 V is 40 amp, which is more than even a 20A circuit found in modern kitchens.
It'll require something like a dedicated 220V/30A line used for a water heater (again, in the US), which will handle 6kW. Again, not something I think feasible for most people renting an apartment.
Says an electric heater (not infrared) sauna is about 4.5kW (about half my shower), takes about 40 minutes to heat up, then 20 minutes in it, so say 5kWh if you time it right, maybe 8kWh if you have a longer time in it or aren't perfectly tires. Even at current uncapped UK prices of 60p/kWh that's about the cost of a takeaway coffee.
I'd use a sauna a lot more if the UK were like Germany (I was in Munich recently for work and used it every day), however there are rarely saunas in UK hotels, and those that are require you to wear clothes! Sadly haven't got enough space at home for one.