KANSAS CITY, Mo. -- The last three times the Kansas City Chiefs traded for a starting quarterback, they parted with something of value in return. They gave up a pair of second-round draft picks for Alex Smith in 2013, a second-rounder for Matt Cassel in 2009 and a first-round choice for Trent Green in 2001.

Now that it may soon be the Chiefs’ turn to deal a starting quarterback -- and one who was the NFL’s top-rated passer in 2017 -- their fans have a vision of a bounty that Kansas City would acquire for Smith, if in fact he is dealt this offseason.

That’s unlikely to happen for a variety of reasons, none of which has to do with the way Smith played in 2017. The price the Chiefs would eventually extract if they do trade Smith would revolve more around Smith’s age (he will be 34 in May), his contract (it expires at the end of the 2018 season), and the fact that a number of quarterbacks appear headed for the market in 2018.

The Chiefs could hold onto Alex Smith if they don't get an offer that moves the needle. AP Photo/Julie Jacobson

Good old-fashioned economics -- supply and demand -- will ultimately keep the price down.

“That’s 100 percent true," former Tampa Bay Buccaneers general manager Mark Dominik said. “When you look around the league, there are only about five or six landing spots and you have to realize some of those will be taken by draft picks. There are three or four quarterbacks that a lot of people feel are first-round guys. That cuts into the chairs at the table and [Washington’s] Kirk Cousins is going to get a seat at somebody’s table.

“So you’re talking about maybe two or three real possibilities at the most, and at that point, what leverage do the Chiefs have?"

Trades involving a starting quarterback don’t happen much. There have been three such trades in the past three years.

Two involved Sam Bradford. He went in 2016 from the Eagles to the Vikings for first- and fourth-round draft picks. Bradford was sent from the Rams to the Eagles the previous year for another quarterback, Nick Foles. Two draft picks went to the Rams and one to Philadelphia to balance the trade.

Jimmy Garoppolo was traded last year from the Patriots to the 49ers for a second-round draft pick.

The price the Eagles received in the most recent Bradford trade would seem to be the most applicable to what the Chiefs might be able to extract in return for Smith. But a number of factors were in play for that trade that won’t be in any Smith deal.

Bradford was 28 at the time of the trade with two seasons remaining on his contract. The Vikings paid him $25 million over those two seasons. Smith is scheduled to make $17 million next season in salary and bonuses.

The Vikings were also desperate at the time of the trade, shortly before the start of the regular season. They had lost their starter, Teddy Bridgewater, to an injury and paid a premium to acquire a replacement at that time of year.

The Garoppolo trade for a second-round pick wasn’t friendly for the Chiefs in this case.

“The Jimmy Garoppolo trade just reset the market," Dominik said. “You throw in [Smith’s] age and the length of his contract and the salary-cap aspect and it’s easy to say, ‘Well, if Garoppolo is a 2, then Alex Smith is a 3 or a 4 because he’s a 30-something-year-old with a high salary and I might have him for only one year.’ There’s no reason to give a premium pick for that."

In their recent trades for starting quarterbacks, the Chiefs identified those players as targets early in the process, perhaps increasing the price. Green had a previous association with the Chiefs’ coach at the time, Dick Vermeil, and Cassel with the general manager, Scott Pioli.

Green (30) and Cassel (26) were younger than Smith is now. Smith was 29 when acquired by the Chiefs.

This year, at least four quarterbacks probably will be drafted in the first round: Wyoming’s Josh Allen, USC’s Sam Darnold, UCLA’s Josh Rosen and Oklahoma’s Baker Mayfield. Several veteran quarterbacks who started at some point in 2017 also could be available. That list includes Bradford, Cousins, Miami’s Jay Cutler, Minnesota’s Case Keenum, Buffalo’s Tyrod Taylor, and Josh McCown of the New York Jets.

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The supply may well outpace the demand, which is why Dominik said he believes the Chiefs are better off keeping Smith than dumping him for whatever they can get.

“I wouldn’t think the Chiefs would have a lot of leverage in this case," he said. “I wouldn’t be too motivated to do anything if I was the Chiefs.

“You never know. Maybe the value of Alex Smith actually increases once training camp starts. Maybe some team loses its quarterback in camp or early in the season and they’ll give you more than what you could get now."

Keeping Smith might not be practical. Patrick Mahomes looked like he would be ready to take over from Smith. The Chiefs also desperately need the $17 million in salary-cap room they would create by trading Smith.

“If they really want to trade him, I think it’s a mid-round pick," Dominik said. “Maybe a team like Jacksonville might want him and give a third- or a fourth-round pick, something in that range. But not a 1. That won’t happen. It’s not because he’s Alex Smith. I’m not beating up Alex Smith here.

“They’re just going to be hard-pressed to do better than that because of the circumstances."