There was one VERY close election: it was in 2000 where Bush-43 took Florida in a squeaker. Let's do the numbers.
There were six million voters in Florida (6% of the electorate) and because the count was VERY close, the margin was 537 votes. Roughly speaking a Florida voter had, individually, about a 0.083% chance of settling the election. If we assume that the person assessing the probability thinks a razor-thin election is likely, but doesn't know whether the voter's state is a key swing state, we can call it a one-in-20,000 chance of swinging the election.
But that's for an extremely close election. More plausible is to say you have one chance in-a-million to affect the outcome in a swing state, zero if not a swing state.
Is it unusual that a SINGLE state will decide the election? Elections are EXTREMELY close overall -- especially in SOME venues -- in post-rational Amerika. There is indeed a reason for this! If the election is close but red-shirts are winning, things may go peacefully. The winning margin is whatever. But a close election that favors blue-shirts will be quite different. Red-shirts will litigate, throw accusations of cheating, and cheat themselves. The result is that close elections are more common than normal statistics would suggest.
Here's a moral dilemma. Suppose a voter lives in a swing state; is planning to vote; but is offered $10 not to vote. He says $10 cash is worth more to him than a lottery long-shot at selecting POTUS and accepts the offer. (But $9 would not be enough.)
But if gambling expectations are linear, and the chance is one-in-a-thousand instead of one-in-a-million would he need $10,000 not to vote? Or $10 million if offered the fact (1-out-of-one) of declaring the POTUS winner?
There are various ways to frame the scenario. Ask a Trump supporter if he would take $150,000 if he would agree to make Biden winner. Explain that it's the only way to "stop Trump." Most would accept the offer (at least if they could keep it secret from their friends). Yet (assuming linearity) that means he considers his normal vote to be worth only 15¢ (or even less in a non-swing state), hardly worth the expense and bother of starting his car engine.