Don't they charge you more if you do pay-by-plate though? I always see signs that have a price with local ez-pass, a higher price with out-of-state ez-pass, and an even higher price for pay-by-plate.

Yes, bill for plate OCR is typically a lot more expensive in addition to having to logon to a site etc.

Ez pass billing is all over the place, each state/authority does whatever it wants.

If you reg a secondary car’s plate to an ezpass account without using the transponder, a lot of states will just think it was a read fail and charge you the regular rate but it depends.

The less honest states (New Jersey, probably others) will charge you a punitive fee (which doubles if you don't pay on time) for not having an EZpass on that vehicle. And then when you call customer support they'll argue with you, until you call on the last day when they finally agree that everything was good and proper.

In Washington it's just 25 cents higher (if you're registered -- $2 higher if you're not registered) than without a pass. Not a huge deal.

25 cents for me. I can get a sticker for $5 sticker that negates that (no transponder I think for Seattle’s first 520 bridge, maybe for carpools?). Oh, supposedly the sticker is a transponder, so I can save 25 cents if I buy a $5 sticker. Even though I don't use the bridge that often, it makes sense to buy.

Ussally if you don't have an account they charge you more. But at least for the systems in my area they'll charge your account wether you have your toll transponder or not (because they OCR your plate and charge the linked account)