I looked into the "cheapest" upgrade, a pair of ergons, but finding the Nexus/Rohloff style for my single shifter is proving to be a pain.
Why? they are stocked by Multiple distributors to Bike shops in the US, (& online retail sellers)
I also see them shipped out of SJS in the UK, anywhere on the planet if not in NA.
NB you can get the standard full length, and cut one shorter.. as well the 2 shorter
and add a few wraps of bar tape to feel longer ..