Cost-Conscious Bode Plotter

In my quest to design and build high frequency devices, one useful piece of kit would be something that can measure the frequency response of a bit of circuitry.  I think that this is one of the main functions of a device called a Network Analyzer -- but those are quite expensive tools.

It seems interesting to try to build something that performs just this one task, and (through this focus) keep the costs down.

So the idea is:

1. Generate an accurate sine wave in the range of (say) 1 kHz to 100MHz or 200 MHz.  I don't have the chops yet to deal with signals in the GHz range, so I'll start with a more manageable frequency limit.
2. Amplify the signal to a selectable voltage level.  Probably 5V - 10V is sufficient as a maximum, and for a minimum, whatever I can manage (ideally maybe 10mV or so).  For this purpose, it seems like being able to deliver the signal into a 50 ohm load is good enough, so 100-200 mA of current seems like a good goal.
3. Deliver the signal to the Device Under Test.
4. Probe the DUT at a desired point and deliver the voltage signal back to the test unit.
5. Measure the peak and/or RMS of the return signal voltage.
6. Perform this test repeatedly with different frequency values, under processor control.
7. Display the resulting plot.