Class cost is BP cost to build the ship.
But, it's not quite as bad as you think. The overhaul per year cost is the cost to spend a year in overhaul...which would knock 3 years off the maintenance cycle time.
What's going on is this: if you keep a ship maintained by parking it over a maintenance location, its cost over time is 1/4 its BP cost in MSP, every year.
If you keep a ship maintained via periodic overhauls, you pay an average of 1/3 its BP cost in MSP for every year of existence. Plus MSP expended for maintenance failures.