although i don't use UniRGP, i cant imagine it would be super easy. Since plygame has uGUI support and the example UI is all done in uGUI, it would be easier and quicker to spend the 38$ on plygame and run with it. has all the blox for uGUI, etc. worth the investment imo.
I guess it all depends on how complicated you want to make your UI. I'm guessing there are also more examples for plygame, so you can setup your own UI or leverage the sample UI Leslie provided in plygame (RPGUI).