Unfortunately, ZOOCONN is correct. People complain about UConn prices, but BC tailgating requires a donation to the Flynn Fund and the minimum donation for a tailgating spot is ~$1500 per season and you could pay $10k per year or more. For visiting fans, BC is the worst college football experience, unless you have BC friends that have a tailgating spot. (Years ago, it was not as bad.)
Below is the link for BC/UConn parking options for visitors and the Flynn Fund on-campus football parking map (with pricing). You could tailgate in the Comm Ave. garage for $400, but no grilling is allowed. My suggestion would be to buy a parking pass in Waul House parking lot for $75 which is close to the stadium. It is a non-tailgating parking lot, but you can just drag your beer and food to a patch of lawn in a tailgating area that allows you to eat and drink. You could park in Lower Brighton for $50 which is a no tailgating spot and try to drag your stuff to a location that allows tailgating. The other visitor lots are non-tailgating and you have to take a shuttle bus to campus.
All that said, you can try to sneak onto a tailgating spot on campus, but it is not easy and I think you have to be pretty early. One of my BC friends uses the same spot for every game and they do not have a parking pass. We have joined them by parking at the Riverside T station and taking the T to Chestnut Hill or Reservoir stations.
UConn Game Day Parking
Seating and Parking | Boston College | Flynn Fund