If you're choosing a neurotoxin off the per-unit price on the distributor invoice, you're being marketed to, not informed. List price is the most visible number and the least useful one. The figure that actually decides which toxin makes you money is loaded cost per clinically equivalent treatment, after dosing conversion, rebate capture, and duration.
Start with the trap everyone falls into: comparing the ~$10–12 per-unit feel of onabotulinumtoxinA to the ~$4 per-unit feel of abobotulinumtoxinA and concluding the latter is "cheaper." Those units are not the same size. Dose conversion alone erases most of the apparent gap before you've accounted for anything else.