I've seen one-ways price on Hertz 3 different ways:

1) Higher base rate (like ~$80-$100/day) with free mileage. Works well when we do a long 1-day drive, but don't need the car at either end.

2) No free miles ($.25-$.29/mile). Better when keeping the car for a couple days, but minimal extra miles beyond the main drive.

3) Treated as if the same location -- this is true for some places on some corporate rates (e.g. I can apparently rent in Sacramento or the Bay Area and drop off anywhere for the same price). This past summer, on a non-corporate rate we rented from a PHL-area suburb HLE and returned to PHL airport on a local-like rate (but renting from the PHL Amtrak station and returning to PHL airport would have been much more expensive).

I've never seen an explicit "drop charge", though they might exist -- perhaps as a penalty for returning other than where the contract states.

Sometimes whether #1 vs #2 comes up varies depending on the day and location (which HLE, for example). Unfortunately, I don't know how to force one or the other -- if it makes a difference to your usage, you can try to plug in the "rate quote" from one search into another set of dates/times.