>Also in 1997, the facility was renamed Qualcomm Stadium after Qualcomm Corporation paid $18 million for the naming rights.[8] The naming rights belonged to Qualcomm until 2017, after which the rights were purchased by San Diego County Credit Union.

Surprisingly cheap! Not that I think it is a good use of money, but less ostentatious than I expected.

I assume naming rights would cost a certain amount per year.... Not be something you can buy and then potentially resell later for more money.

Pretty sure most sponsors would include an exit clause just in case. Sure there would be penalties, but if the stadium can re-lease for more, they should play ball.