There's two aspects to your question, (1) the immediate maintenance, and (2) the eventual maintenance. Depending on the reliability of the seller and the maintenance taken, hopefully it won't need anything, but if you don't know, you're going to probably want to change all the fluids, fuel filter, spark plugs, spark plug wires, air filters (or clean, depending on type), etc. and at least inspect all the wear items (brakes, tires, etc.). Eventual maintenance is generally like any other car, except that there is more fluid for things like oil so that costs a bit more (plus you may use better oil than your other vehicles, so even further costs), more spark plugs than a regular car, etc., plus tires are way more expensive than regular cars. Finally, anything that breaks that is not a maintenance item will likely be a lot more expensive than a regular car (e.g., transmission, window regulator, etc.).