If you will click on your Gerber System Tray icon and then select Install Plotter / Router, you will be shown a list of selectable plotter models which number in the dozens. Any number of them are manufactured by Roland, Graphtec, Summa, Allen Datagraph and others. Once selected they will respond to a Gerber PLT file sent from GSPPlot. It is possible that some special features of any given plotter may not be fully supported but the job will cut.
I have several friends who have reported success with the Graphtec line. You may find that limiting your search to only a 30" plotter may rule out a number of plotter models. It would be wise, IMHO, to limit your selection to what is supported on the above mentioned list.