For some reason the Hit-A-Thon jogged my memory on one that we kicked around for a LL fundraiser at one point. Could easily be modified for a HS fundraiser. Basically a "night at the fields". Invite the local LL kids to hangout at the fields with the HS players. Charge $5 to $10 a kid or so. That includes some instruction time with the HS kids. Maybe put them at stations or something to work with the kids. A mini-scrimmage game on the HS field and then to cap the night off, rent a blow up movie screen (or use something attached to the backstop) and show a kid related baseball movie. You could also setup concessions at the field and movie to raise even more money.