Utah Trikes carries a set of 155 mm Mtn bike cranks for $75, but you'll need to buy sprockets because they are 4 bolt.  Cat is 5 bolt.
 
More then likely you'll need the bearing kit for bottom bracket too.
 
We bought a 150 mm Divinci set from Hostel Shop, with bearings its about $200.  Cat sprockets fit OK, but you'll also need 5 1/8" spacers for low gear.

Thanks Jay, I found all those same things...big investment that we can try out first...was trying to see if any one had some to try and see if that would help the situation.