The best way to keep future maintenance to a minimum is to make sure it's running well in the first place.

When you get it, give it a good going over and fix any niggly problem it may have. Get it compression tested to give you an idea on ring/piston condition etc.

Change the gear oil before you go anywhere. If the oil that's in there is really mucky then it may be worthwhile to change the oil, then change it again almost straight away to flush it out. You'll then be safe (ish) in the knowledge that it's clean and slippery inside there.

Also, drain out the 2T oil and refill with a quality brand, even if the previous owner insists that he used the best stuff. You never know what's really in there and a new top end is far more pricey than a litre of two stroke oil.

Same goes for the coolant. Even if it looks green and clean, flush it through and refill. Check coolant level immediately when you start the bike for the first time (before the water gets hot) and top up if necessary.

Change the brake fluid, check pads, adjust the chain tension if necessary and give the tyres a kick.

When you're satisfied that it's all good fill it up with juice and take it for a spin.