Run two of these for $156.
These would be great for a 48v system because the low cut voltage usually around 42v is in line with the 3.5v/cell generally used a max discharge. You can run em on a 36v or even a 24v if you use a voltage alarm to alert you on the low voltage cut. Cost about $11 and runs off one of the packs balance plugs. The motor doesn't care how much voltage is put to it with in reason, usually depending on phase wire size. Most controllers have 63v caps so they easily handle close to that. Its just the LVC that is different and of course max amperage output. A 24v controller will have slower acceleration and hill climbing than a 48v because the 48v has a higher max amperage. However the 24v controller will still give the max voltage.
I have one total(motor/controller) 24v system that I run on 12s which is 50.4v off charge. Never had an issue with it.
Moral of this story is with in parameters you can pretty much do what you want with the systems. There are some modded 9c 48v hub motors running over 100v over at the Sphere.