There is a Chinese guy on diyaudio.com who sells curve tracers. I bought one from him around 2-3 years ago but I didn't get it to work, not because there is something wrong with it, but because it requires "some assembly" and I haven't had time to do it. The Peak DCA Pro can also do curve tracing and it is relatively inexpensive. The only problem I've found with it is that it is not capable of injecting large currents or producing large voltages, so you can only test components at low currents and low voltages, I don't know if the latest versions have improved in this respect. Large currents are only needed if you are doing power amp stuff, but large voltages (higher than 12V) are required in the pro-audio world, since it is by no means unusual to find +/-24V discrete circuitry. However, do you need to plot IV curves for voltages higher than 12V? It might not be needed, but, again, it depends.
In general, the major problem with curve tracers are BJTs, because they require very low currents at the base, FET's in general are very easily characterized with any 2 channel programmable DC Power supply, in fact, a good 2 chan programmable DC power supply is, in my opinion, the best thing you can buy; it will allow you to test any component, and you will be able to plot IV transistor curves with it, but they require some sort of software platform: you can use MATLAB/Octave, or Labview, or whatever, but there is some programming involved and you might not like that. Also, many require a GPIB to USB interface, which is
very expensive (although other brands have lower cost solutions), others require a simple RS232 serial port or Ethernet, which is cheaper. However, the main problem is that not many programmable DC power supplies allow you to limit currents to a few microamperes (the opposite problem of the Peak DCA Pro), which is the required current value for BJTs at the base. When testing power BJTs this shouldn't be such a big problem, since base currents can be in the order of hundreds of microamps to miliamps.
So, to sum up: if you are not dealing with high currents/voltages, go with something like the Peak DCA Pro, otherwise, go with a 2 chan programmable DC power supply, or Peak DCA + prog. DC PSU if you need both. You can find used HP programmable DC PSUs on eBay for like 100-200 USD.
