New enclosed buggy: $5,000-8,000. Used: $1,500-3,000. Repairs: $200-500/year. Total: $400-600/year (over 20 years).
Comparison
Average car: $35,000 new. Gas: $2,000/year. Insurance: $1,500/year. Repairs: $1,000/year. Total: $6,000-8,000/year. 10-15x more expensive than a buggy.
But
Buggy doesn't go to another state. Doesn't haul a ton. Doesn't work in rain (well, it does, but wet). Amish know this. And still choose the buggy. Because money isn't the point. Community is.