Cho makes a good point, that baseball is still cheaper than other pro sports. It's also far cheaper than college football. When I was at Michigan, students tickets (i.e. the cheapest ones) were $50 apiece, and you had to buy the whole season. Taking a family of four to a Michigan football game is surely well over $300 these days. (Taking a family of four to a Michigan basketball game, ehhhh, perhaps a little less....)
Or consider the movies. If tickets are $9 apiece, and one buys four sodas and four containers of purported popcorn, it could easily cost $60 to see a movie.