It's been my experience after 130,000 miles or so (depending on upkeep and how it's driven) a whole litany of stuff needs replacing. From the radiator, through the front axle u-joints, unit hubs, rear brake cylinders, exhaust, catalytic converter or worse. None are actually deal breakers, but all require additional bucks along with the purchase price.
I tend to think of the initial cost as the purchase price and the first year of ownership. I don't think I've ever bought a used XJ that didn't need a grand worth of parts the first year or so.
XJ's are gas hogs, it's a buyers market.