Yamaha DTXpress/DTXplorer/DTXtreme

hello,

i'm new to the list and digital drums. i recently bought a yamaha kp-120 
kick pad (real head) and now looking for a inexpensive drum module only 
for the bass drum. i'm not going to buy hihat, cymbal or snare pads.

what module would you recommend to start with, which fits to the kp-120? 
i don't care, if it's a alesis, roland or yamaha. and don't want to 
spend more than 200\ufffd for a used one.


i hope it's not off topic to ask this kind of questions here and to talk 
about DTXtreme hardware.


thx,
-s