which life and lipo batteries are you looking at and how many?
One other consideration is efficiency, higher loads affect lead far more than lithium due to the pukert effect. So weight, lifespan, efficiency, cost per mile, performance, how many reasons would you like?
Yes the charger/bms does add to the cost, but just so you know, you can trade convenience/time for cost there as well. If you have a suitable 3.7v charger (i.e. for one battery or collection in parallel) you can balance charge the whole pack by simply charging each battery one at a time. When you make/build a second one, it will take half as long, and could be controlled by a relatively simple box of chinese relays and a microcontroller.
Continuing to add 3.7v chargers gets inefficient though, as you take 120v down to 4ish volts several times, each at the same current that you could apply 72+ volts across the entire pack. Though you still have to monitor the individual voltages to prevent overcharging one of them.