You do not have to sell your car for any amount of money.
I have news for you. The OP has already sold the bloody car!
That is unless you've somehow managed to neuter a fundamental principle of contract law; like that known as
offer and acceptance?! And repeal specific portions of Oregon's Uniform Commercial Code!
ORS 72.2040 Formation in general. (1) A contract for sale of goods may be made in any manner sufficient to show agreement, including conduct by both parties which recognizes the existence of such a contract.
If the OP refuses to deliver possession and endorse over the title, then the buyer has a cause of action FOR BREACH OF CONTRACT. But not for SPECIFIC PERFORMANCE of contract! *
The buyer's measure of damages would be the difference between the agreed selling price of $325 and the cost to replace the vehicle with one of comparable vintage and condition. If the difference is negative, then the buyer has no actionable claim simply because he would have suffered no damage.
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Incidentally in the matter of the statute of frauds - in Oregon only those contracts for the sale of goods for the price of $500 or more need be in writing.
ORS 72.2010 Fundamental Requirements - Statute of Frauds
[*] For OHR's edification an action for SPECIFIC PERFORMANCE would not lie in this instance. Not unless there was something especially unique about the vehicle such that it could not be reasonably replaced.