The dealer told me verbally that the charge was 1/4 cent per mile.
I'll bet you a 1/4 of a cent that the employee of the dealer whom you claim said this will deny having said it.
It didn't seem unreasonable to me at the time, as I wasn't aware of market rates for excess mileage charge.
Yeah, but think about it. At 1/4 cent per mile, being over by 20,000 miles (which is more than most folks drive in a year) would only cost you $50. A year-plus worth of mileage for only $50? I submit that no reasonable person would believe that.
It seems suspect to me that all other amounts in the contract are prefaced with a "$", whilst the excess mileage charge is not. If I was cynical I would say this was intentional.
You can make that argument. It's not implausible, but I don't expect it to carry the day. And I disagree that this hurts you more than it helps you. You have an ambiguous provision in the contract. With a form contract, ambiguity is construed against the drafter. The argument is that the drafter clearly knew how to denote dollar amounts, so your argument is, as you stated, that this omission of the "$" must have been intentional. The dealer's argument will, of course, be that it was inadvertent (which it likely was) and that no reasonable person would believe an overage charge of only 1/4 cent per mile.
It appears the contract also has an arbitration clause, at the option of either party, which I expect will be exercised.
Arbitration will be less favorable for you than small claims court.
Here's the bottom line: When you return the vehicle, the dealer is going to expect you to pay 25 cents per mile. The dealer is not simply going to accept what you have claimed in this thread. If you don't pay, you are going to be sued or have arbitration initiated, and you will very likely lose. Maybe...
maybe...you'll be able to convince the dealer to accept something less than 25 cents per mile to settle the matter (e.g., 20 cents per mile).
2 - Read your contract. Find the place that says something like "This contract is the only agreement. Anything said outside the contract doesn't count." Or words to that effect.
I agree that it likely says this. However, in this case, the contract contains an ambiguity, so extrinsic evidence can be admitted despite the existence of the integration clause.
You are going to have to have a lawyer in that arbitration and any subsequent lawsuit.
Arbitration, if it happens, is going to be binding, so there won't be a subsequent lawsuit. Also, any lawsuit would almost certainly be filed in small claims court where lawyers aren't allowed to represent parties.