you need to raise your budget bit more if wanna buy brand new...
buy used, its still slightly above your budget from the couple few local online ads which i noticed from the last 1-2 years...
cheapest not too sure, but if looking at the roland vg/gr series, the gr20 cud be.
If wanna brand new, sweelee seem to be the only place i've seen selling those roland.
Anyway, if you can find someone selling the geetar synth, do check if the midi pickup(gk2a or gk3) is included as well, if not, you will have to spend bout another 200+(rough figure) to get a new one from sweelee