That's undoubtedly, true. However, a lot of those non-league sides are based in areas with much larger populations. The % of people from Motherwell who go to games is pretty much in line with other towns and cities.
My local non-league team used to be Forest Green Rovers. Their cheapest season ticket this year is for the terracing - 280 quid for adults, 240 quid if you bought it before June 30th. It's a nice wee ground - holds about 5,000 - and a good day out, but definitely not cheap.