One of our most successful was when we were a small pack (13 boys or so). We rented a group cabin at a state park for 2 nights in the summer. There was a small water play area, plenty of activities offered by the park, and just time to hang out and enjoy the company. We had almost all of our families attend.
We've also had some great campouts, though this past year our campouts were sparsely attended - in part due to the weather.
We go to SpaceCenter Houston once a year. THey have programs for Bears and Webelos. Pricey, but usually well-attended and enjoyed. Every other year, we go to a WWII destroyer that is docked about an hour away on the Mississippi River.
As far as the money goes, for the group cabin, I think we charged $5 per person. Space Center Houston is $50 per person and parents are required for each boy. If you want to play, you gotta pay. The destroyer is about $16 per person, and I think those participating pay for that, too. Sometimes the pack will pay a certain amount of the cost, and the parents will supplement the cost.
We require parents at all of our events, so it is never a problem getting enough parents. You want your kid to come; you come, too.