my place was built in 1902, 1t's 800 sq feet apartment. I have nobody upstairs and a max of r-17 (as low as r-5 in some areas, that's one interior wall worth of insulation) in any direction other than my next door neighbor. All electric, my bill was $78 last month. It's as low as $30 when I don't use HVAC in the spring and fall.
I have seen over the years of working on electric only heated places bills in mid winter 50-100 typical but up to 250 a month in greeley. The variable here was the users, not the structure or equipment. Although this month the meter reader has screwed up and had me dealing with a ton of extremely high bills with no logical reason.
Want to try it yourself? Go to wal mart and buy the oil filled 110v space heaters at $33 per, try it for a month in your place with your usage. 110v is slightly less effecient than the 220v heaters you'd have in those houses. Just put one in each exterior room and turn down the thermostat for the central unit.
https://www.walmart.com/ip/Oil-Filled-Heater/53017084
Personally if I were looking for a house I would only get one with gas forced air AND a wood stove, and keep several of the above heaters on hand along with spending money and time dealing with insulation and air flow as soon as I got the keys, the faster you fix this the sooner you start getting a savings. With a strong preference to unfinished basements so I could access the duct work to correct issues.
Excel used to offer an average use quote, you could call them and give them an address and they would give you an average bill based on the past 3 years broken down by winter/summer. They've stopped this recently but your utility company may offer it? Worth a call.
Also semantics but boilers are for steam heat, not hydronic heat. Those are just hydronic heaters but slang is boiler but it will cause severe damage if it boils.