All I can say is make sure you get a really thorough Pre-purchase inspection. an unmaintained 540 will nickel and dime you to death. Don't let a cheap purchase price fool you.
Get one with a good service history. If the entire cooling system hasn't been replaced within the last few years, replace the whole thing as soon as you buy it.
Expect a set of rear tires a season, and $100+ oil changes.
I'm not trying to scare you away, because I love 540's. but I don't want you to be surprised when you find that this isn't a super cheap daily driver.
If you're interested, I can give you a breakdown of my service history, which might give you a better idea.