The silver truck, named Snakebit, went up for sale Friday at auctioneers Barrett-Jackson in Arizona and was bought by Gord Broda, a businessman from Prince Albert, Sask.
The hospital is in Saskatoon, where Simmons' wife, Shannon Tweed, grew up.
Saskatchewan Premier Brad Wall had said the highest a '56 Ford has sold for at Barrett-Jackson was $180,000, though he hoped the auction would raise even more money for hospital equipment.
Wall was at Friday's auction, which was broadcast on Fox Sports, and tweeted pictures of the celebrity couple standing in front of the vehicle and himself posing with Broda after the purchase.
Snakebit was built in Saskatoon and the front end of the revamped truck is a Shelby Mustang.
Wall — a self-confessed car nerd who owns a 1967 Dodge Coronet — said even though he's not a Ford guy, the truck is beautiful.
Before the auction, Tweed addressed the crowd and explained her passion for helping the children of Saskatchewan.
"I was born in the province called Newfoundland," she said. "My mom had to move with her seven children back to a province called Saskatchewan. She started working at a hospital; she became head of the hospital. So I was keenly aware there was no children's hospital in our town and it's a shame. We're one of two provinces in Canada that doesn't have one, and we're going to try and make it happen tonight, with your help."
Bidding quickly rose to more than $350,000, then went even higher when Simmons promised to throw in a signed guitar "and a lap dance" as part of the deal.