Automated Approaches for Measuring Audio Amplifier Frequency Response
Rightmark Audio Analyzer is a free tool for performing frequency and distortion measurements on audio equipment using a sound card (or any recording device that can save PCM). 

If your goal is only to measure frequency response, almost any laptop would be sufficient.  Hook up the line out from the laptop to the input on your device under test. Then take the output from the DUT to your line in.  Set the sample rate you want in Rightmark and hit go.  It'll take a few seconds and then give you the transfer function of the device (as well as a lot of other information you may or may not have a use for).