The headless systems can be really expensive- The Steinberger jobs that Hohner used can be bought as spares and are about as cheap as I have found for a 5 string. But the main problem with those is that the headpiece only accepts double ball end strings which is not an option on this short things. Hipshot do a headpiece but is very expensive, ETS do one which is more reasonably priced, but there isn't a massive choice!
For the four string ones in this build are using the bridges widely available on eBay and are very reasonably priced - but they don't do a five string version.
I have come across another supplier of headless parts that are comparable in cost with a decent standard headed bridge and tuners. So I've taken a punt as it looked interesting (and the guy that makes them has been helpful).....
More details to follow...