Yamaha DTXpress/DTXplorer/DTXtreme

Hi,

I have a DTXpress II set and want to expand it to have double bass.

Any recommendations for a non-expensive double bass pedals.

Also, I was toying with the idea of buying a KD7 trigger with a 
single pedal and chaining it into the Yamaha kick tower. Has anyone 
tried this? Does it work well?

Has anyone used the Pintech ergokick? howz that one?

Thanks,
Anand