For me, the tank plus installation was almost $10k CAD, and then the septic field itself would probably run between $30k and $50k CAD. So to be generous we could say $50k total for the full install. So that's about 8 years at $300 bimonthly just to pay it off. And you'll need to get it pumped every 3-4 years depending on tank size (a couple hundred bucks). And the field won't last forever, so in about 25-30 years probably looking at major repairs or even replacement of the field.
Then we get to the well... Also not inexpensive to install... But varies a lot depending on bedrock depth, etc. But probably $20k to install. And then you'll probably want water filtration... because do you trust your neighbour's septic systems? :-)
Should you really like nature and having space and big gardens and farming and the like, then be prepared to pay for it.
Not sure how they fare long term, but the septic isn’t the only option if you don’t have sewer available.
I do not especially like tiny houses on wheels, but I think I could live comfortably in an 800sf small house on a rural piece of land.