One-way rentals are unlimited miles if it's with a CDP with gives unlimited miles, such as AAA. Many flat rate corporate CDPs by contrast come with a mileage charge.

If you are a member of AAA, I suggest using your Club code, and checking Hertz's website to see if your one-way qualifies for a coupon. (Some coupons are roundtrip only, some are one-way only, and some work for both, as described in their respective T&Cs.)