That's too much for a unit that may have a difficult to repair issue--and yes, proprietary parts may be involved an it is definitely not a calibration issue. It is a later model, US made, Agilent version, so that is a plus, but broken, no bumpers/handle. $250US is just too much IMO. I recently posted an auction (in France, unfortunately for you and me) of NEW old stock 34401As for $400US. Those got snapped up (50 of them!) If you look at sold units on eBay, you'll find a pretty nice one went for $350US and a broken one with what is likely an easier fix went for $150.
If you are on a tight budget and you want a simpler meter but with diode testing, the Fluke 8840A/8842A series has a "hidden" diode mode that is actually documented but not on the front panel. You simply select the 2K resistance mode, the test current is 1mA and the reading in k-ohms is your forward voltage. It works up to 2V. You can probably find a working model with AC (AC was optional, make sure you get it) for what you're going to pay for the broken 34401A. Of course the 34401A is more advanced, has serial comms and menus full of slightly more advanced features (the 8840 series doesn't even have min/max or a beeper...) but if you want one, get a decent one.