About 250 companies are paying millions of dollars to do business out at the U.S. Open, CNBC's Darren Rovell reports.

Largest spenders are shelling out $200,000 for their hospitality tent. Meals are costing roughly $130 per person and some companies even spend an extra $95,000 to make their tent look more attractive.

“You might say $200,000 for a tent is a lot of money, and it is!” said Mimi Griffin, director of marketing in the U.S Open Championship.

“Except when you break it down on a cost per person basis, you’re talking about 100 tickets per day, seven days," she added. "You’re talking about a cost of maybe $250 to $350 per person. And if you have a company or client that’s bringing tens of thousands of dollars in business, of course you’re going to spend that kind of money on them.”

Around 60% of the companies who have tables and tents are located in the Pittsburgh area near the Oakmont Country Club, while the other 40% are national. But they all say it’s hard to even estimate return on investment.