The Agilent 82357b can be found on ebay for $80 USD. Some
are known to be fakes, but they are very good fakes that duplicate the circuit, including PCB layout, exactly. Same microcontroller, same true GPIB bus driver ICs. They work identically to the originals are far as anyone can tell, which is to say that they work very well. The Agilent software provides full VISA and gpib-32.dll programming interfaces, so is compatible with all software that expects those standards in place. Notably, the prologix does not have such support (nor true GPIB bus drivers) and this should be a consideration.
I use mine under windows with Activex/COM controls, which allows me to interface to the adapter/instruments with vbscript or jscript within html applications (html application or .hta is really just a html file or web page that runs with the full permissions of any other application). This allows for almost too-easy GUI creation, if you know a bit of html. An advantage of the VISA/GPIB-32 support is that when I switched from a NI GPIB card to the Agilent USB, the scripts all worked just as before.