I just bought a couple of bench top meters on Ebay that I think turned out to be a pretty reasonable deal.
Both combined were $60 US + $10 US shipping.
The first is a Keithley 175. The only issue that I have with it so far is it doesn't seem to want to come out of Auto Range. Selecting a range button doesn't seem to do anything, and "Auto" is shown on the display. Even with that, checking it on my voltage standard (Fluke 3330B) I get the following measurements.
Voltage Standard Setting Measured Voltage
100mv 99.95mv
1V 1.0002V
10V 10.002V
100V 100.02V
999.9999V 1000.2V
I would say that is pretty darn accurate for a 20+ year old instrument. The only other issue that I have is a cracked case.
The second is a Keithley 191. The main problem that I have with it is fluctuations, ie., the measurement isn't steady. Here is what I measured.
Voltage Standard Setting Measured Voltage
100mv 101.948mv - 102.031mv
1V 1.00593V- 1.00636
10V 10.023V - 10.096V
100V 100.31V - 100.81V
999.9999V 1004.32V - 1004.84V
I'm thinking maybe a few faulty electrolytic caps in this instrument. Though the measurement is close enough for the hobby stuff that I do, I really want it to be stable. This should be a fun one to work on.