i seriously woul keep away from groove boxes all together (again talking from experience) they tend to be a bit gimmicky and not a serious peice of kit (even more so now with D.A.W's as you can do so much in say ableton or cubase). i use the korg MS2000R and that is not a bad synth at all i can use it to make nice bass lines and lovely bleepy rythm parts and some sweet leads. you can pick up one of those on e-bay for about £250.00 - for rythm hmmm not sure i use VSTI's have no hardware (well i have a korg es mk2 but i hate it) but my mate uses elektron and i want one - infact it is the only sequencer/groove box that i here get highly rated (i think that is why they are so expensive).
sorry i could't be more help.
but belive me i (as you) need to consider my budget before i buy anything (the reason i baught the korg myself) but it genuinly is worth saving (even if it takes you 2 years) to get the better stuff cos you will want it anyway a year down the line but you will have wasted £350.00.
it took me 2 grooveboxes to learn that lesson BTW.