The main question is ... does the price make YOU happy?
If that's through their main site, it's possible you could do better using hotwire or priceline. Hotwire has some rates called Hot Rates that show up, and you agree to the price, finish the transaction, and then find out what car place you're getting.
We're trying to decide if we want to use Grayline's
Disneyland Express or get a car, and I check daily with hotwire to see what the total would be. We rented once and it was good, but getting that last minute fillup was a bit scary (neighborhood near LAX we ended up in was a little bit rough)...it's possible we'll pay the fee ahead of time, if we rent (saves time too, we almost missed our plane during that trip!).
Be sure you know if your hotel charges for parking! If you're staying onsite, the Resort Fee includes parking, and everyone pays that fee even if you don't have a car. But a place like the Hilton charges something like $15 per day for parking.
If that rate is cancellable, you can make the reservation then keep looking around, and if you see something better, go for that and cancel the other!