Molly Fitzpatrick at Swimmingly has checked in with every MLB team about the cost of a public marriage proposal at their stadium. Note that five teams do not want to be involved with your personal life at all -- six if you count the Dodgers effectively asking for a second engagement ring payment. Click through to the post at Swimmingly to see what your money gets you in each tier.
I'm kind of surprised the Yankees didn't join their cross-town rivals in banning proposals after this incident:
[youtube https://www.youtube.com/watch?v=WMHidjDB_Uk] [Swimmingly]