The Bears don't own the stadium. The Chicago park district does. The Bears rent from them. The original deal cost I believe 450 to 500 million. The Bears paid for 100 million of the renovation using a loan from the NFL. The city paid for the rest through an increase in the hotel/motel tax.
The stadium is used for multiple events besides the Bears games. Concerts, college football, soccer (the Fire played there up until 2 yrs ago), high school football tournaments, etc. My understanding is they also play international soccer there and that is the reason they won't switch to new turf (because FIFA requires grass).
Peace