Are you wanting a distortion meter or wave analyser or a spectrum analyser?

Also is this for audio or higher frequencies?

I should have been more detailed in my request, I want to study the harmonics in 3 phase AC electrical circuits.

Ohhhh right..... in that case I can't help sorry....

I am lazy/busy so I will not search for. I have used, some 10 years ago, an evaluation board made by Texas Instruments for one of their DSP chips. It was less than $150. It came with pc software. I was able to make decent FFT for KHz waves so, for your application, would be good.

thanks will check it out

You can find test equipment cheaper in surplus Electronic stores I have seen one and bought there.

do they ship to the UK?