I'm not sure about the amount of oil your tractor will hold so it's hard to give a price. As far as what needs changed it needs all the fluids and filters changed.
Engine oil and filter, fuel filters, clean or replace air filter, drain trans/hyd and change filters, front axle and hubs
My L 3000 with backhoe basic cost is, $750. This is the cost includes the oil in the engine, trans, front end, backhoe and the filters.
M 9000 cost around $900
The final cost will depend on the brand of oil and filters you choose to use. It can be done much cheaper than this but I feel it's worth the money to use the best quality lubricants to protect my investment. Not even counting the added wear protection I gain back enough fuel economy to more than justify the oil cost.