I owned a 360 for 3 years, a 2000 three pedal car.
Maintenance - routine is about $500-1000/yr, that's fluids, odds and ends but no major issues.
Every three years is a belt service $3K+ at a dealer, maybe less at an independent.
Every five years is a major service, that's gonna be $5K at a dealer, includes belt service plus a number of other items.
But, beware, routine maintenance comes with a price and more frequently than any car you've ever owned.
clutch - every 10K-20K miles F1 transmission I have no experience with.
brakes - every 10K miles.
O2 sensors - seem to be particularly vulnerable, perhaps due to operating temps, but I put at least two in during 3 years.
Tires - 10K miles, maybe 15 if lucky. All around set is $2k+
Suspension has some VERY expensive bits on it to, the attenuators are pricey, and I've replaced 2. Suspension goes rock hard when one goes out.
And there's plenty more. The guy who just bought my 360 from me had a ppi done, they came up with a list (mind you many were simple cosmetic issues) that was $8K. He's had some other odds and ends done, I figure he's at $11K right now total.
This is not a poor man's hobby.