What Is the Cheapest State for buying an EZPass Transponder

My fam and I will be traveling through IL, IN, OH, and PA in May. What is the best state to go through to get the EZPass transponder? I may never use it again, and plan to return or deactivate it after the trip.

I bought the Uni on Amazon. Runs the EZ Pass system plus whatever Florida has. I originally had a transponder from Ohio which is run by the Turnpike system. The transponder was essentially free but they required a higher minimum balance, higher refill amount and charged a monthly fee if not used. It also had to be returned if the account was closed. The Uni has lower minimums, lower refill amounts, lets you set the refill point, has no monthly charges and is all yours for $15.