MANKATO — “Oh I don’t know. Maybe 400 or 500 bucks.”

That’s what Ben Volkman estimates he and his two young boys will spend in Mankato during the opening weekend of Minnesota Vikings training camp, which begins in earnest today.

A couple of hundred for a hotel through Sunday, he figured, plus some Vikings memorabilia to remember the trip, an afternoon at River Hills Mall and a few restaurant meals — including Jake’s Stadium Pizza, a family favorite.

“We’ve spent a lot more than that on vacations before,” said Volkman, buttressed by his two be-purpled boys who were angling for player autographs Thursday outside Minnesota State University’s Sears Hall.

“So, it’s pretty reasonable.”

When the Vikings come to town, the spending begins.

Thirty-two cities across the country host training camps for National Football League teams and many of them celebrate a similar theme each summer when camps open: local economic impact.

For larger training camp cities, the impacts are muted. But in smaller markets such as Mankato’s, they are significant indeed.

Anna Thill, president of the Convention and Visitors Bureau, said more than 50,000 spectators visited Mankato last year, generating an estimated $5 million in additional local revenue. She said her goal is help visitors find places to sleep, dine and shop while they enjoy their summer stay in Minnesota’s training camp mecca.

To that end, the CVB is coordinating “Jared’s Journey,” a scavenger-hunt of sorts that will lead participants to a host of Mankato attractions in search of a life-size cutout of Jared Allen, the Vikings’ charismatic all-pro defensive end. Thill said clues and instructions will be available all over town as well as on a smartphone application offered through Google.

“Our hope is to get people out and about and experiencing different parts of the community,” Thill said.

River Falls, Wis., was home to the Kansas City Chiefs’ training camp for about two decades — until this summer when the Chiefs relocated to Missouri for preseason camp. (The Vikings’ contract with MSU was extended through 2011 after $400,000 in upgrades were made at Blakeslee Stadium in 2007.)

Rosanne Bump, president of River Falls’ chamber of commerce, said the city held a three-day farm festival this year that attracted about 35,000 visitors to “help ease the pain.”

But, according to figures she shared from a 2005 study, the city will still lose out on more than $1.4 million in local revenue (including $400,000 the Chiefs paid for food and services during that year).

Training camp economics have become so important in Indiana — home to the Indianapolis Colts — that a columnist at the Indianapolis Business Journal called the ongoing pursuit of Colts camp a “civil war” between the cities of Anderson and Terre Haute.

In Renton, Wash., the celebration already has begun for the second year of Seattle Seahawks training camp. With 20,000 visitors expected to attend, the mayor declared today as “Seahawks Spirit Day” and will be flying a specially designed flag above the city hall.

Of course, it all pales in comparison to the economic impacts of hosting a Super Bowl. According to reports after this year’s championship game in February, the Miami area raked in more than $330 million.

“If they ever have a Super Bowl at Blakeslee,” Volkman said, “we’ll be there.”