$200 million is what the would-be San Diego MLS team owners say their stadium (which they proposed to share with SDSU football) would cost. I suppose that's reasonable if it's designed as a 30,000-seat MLS stadium. The San Jose MLS stadium, opened in 2015, seats 18,000 and cost $100 million to build. But SDSU apparently wants a stadium it will control itself (and, I'm guessing, thinks that being a subtenant in a soccer stadium would make SDSU football look small-time).

The better measure is Colorado State's new football stadium that opens this fall. CSU built the stadium on its own campus, so they didn't have to buy land. It has 36,000 seats and cost $220 million. Given the higher construction costs in California, it would likely cost about 50% more ($330 million total) to build the same stadium in San Diego. And AFAIK, SDSU doesn't currently have room on its campus, or any other land they own, to build a stadium.