I just picked up a good used 701 Hotrods crank for $300.
I always thought Hot Rods Cranks were a better than OEM choice but only recently was told that they are made overseas and can be questionable. I have purchased them for my seadoo, old square 701 and now for my new build. I have never had to replace one yet.
Does SBT use OEM cranks or do they rebuild in house? If they are OEM it may explain the cost difference.
If you want more power then now is the time. There are ported 61X top ends coming up on ebay and here quite frequently now. I picked up a nice ported 62T 760 top end for $500 including pistons. Watch ebay for deals and just see what you can pick up.