I do all my DSP algorithm research in Octave, because the price of MATLAB is just too high. I think I'm looking at somewhere on the order of $4k for a single license to obtain the signal processing stuff that I need in addition to the core license.
Would I prefer to have more graphing options, and some assurance that researchers' MATLAB code will work out of the box? Of course!
That said, Octave gets me really close for a fraction of the price. Also, I can peek inside the Octave source and get an idea of how the underlying routines work.