I have a 99 with 110k km on it, since i have it (1 year) the only maintenance I had was to change tires once, change a light bulb, and fix a small vibration problem on the muffler. All that are very random. Open a Bentley Service Manual book and take a look to the maintenance schedule.. add that some money to repair and you'll have a good idea..
you can spend 100$/year for 3 year and then having something changed for 2000$.. it's random.. be kind with your car and she will be kind with you..
at least you know the history so you know you should'nt have to much reparation.. well.. less than if you find another car for that price from a private seller