Maintenance costs are based on mileage and type of driving. Each service requires different items be done. Most schedules are based on 12,000 miles driven per year. At 99,00 miles I would expect coolant and hoses will need service soon , as will the transmission. Suspension bushings and struts are surely needing attention. IF you were to service it like it should I would expect your costs to be high due to the mileage.