I think the only plugin cards for the 3457A are for scanner options, which are of very limited value to the majority of the hobbyists out there.
In my opinion $200 is on the high side, but the lack of shipping costs and risk, and the ability to check it out before you buy is worth a little extra. I would probably check it out and buy it if it produces reasonable values (bring a resistor and a battery so you can test if the resistance, voltage and current ranges are in the right ballpark) if I were in the market for a 6.5 digit bench meter.
An AA battery represents a voltage source that can be used to test all ranges from 3V and up. You can short all of the ranges for 0V reading. A battery plus suitable resistor can form a current source. Shorting the current terminals will give you a second data point. Shorting the inputs can also test 0 ohm on all the ohms ranges, and a suitable resistor can be used to test most resistance ranges.
The 3457A also has an internal self test that at leasts tests all digital circuits (not sure how much of the analog circuits it tests, probably a fair amount).