As I have learned collecting various used/new youth equipment for our 4H program, precision with pellets with the option to also shoot (less expensive) BBs is a false hope. BBs use smooth bore and "precision" pellets use rifled bore. Never the two would overlap unless of course we are not talking about precision. Now I know how I ruined my 760. I shot thousand of BBs because as a kid they were cheap. Live and learn.
Options: Our clubs owns and we shoot the following training equipment.
Best BB: 499B with the micrometer sight. If one is serious about BB gun accuracy this is it for $80.
Best BB/Pellet: 845 with micrometer sight. They actually market this for both BB and pellet and the barrel is smooth bore. Don't expect too much for pellet "precision" but unlike BBs it cuts a clean "non debatable" hole. Repeatable for BBs but not for pellets...but not CO2.
CO2? I don't think what you are looking for exists. BBs are a huge richocet risk regardless of how cheap they are. I would go with a 853C. Repeater (5). Pellets only. Cut targets better, true precision Walther barrel and save money on CO2 powerlets via a single stroke pump. Teach kids the fun of shooting something that can shoot one hole groups at 33 feet. But the little kids cannot not pump it and you have to get out of prone position to pump.
If CO2 is a must I'd go bulk and shoot the 888. After shooting them all I would only povision the club and kids with 499s to start and 888s to advance. After that mom and dad have to write the check.
My Crosman experience/powerlet experience was with a challenger 2000. We had one but it is "big", powerletts for 6 guns on the line added up in $$$. I found myself changing them and getting them in the "sweet" zone/sighted in too often. 300 shots with an 888. I sold it but my perspective was keeping multi guns running.
When I speak of precision here are 6, 10 shot groups with a Daisy 888 with Walther barrel.
http://mysite.verizon.net/durants/images/10pellet.jpgOne member's first hand experience. Glean from it what you want. My recomendation, get a 854 if this is a plinking affair. If this a marksmanship initiative get two guns, a 499 for BBs and then as much gun as you can afford 853 to a 888.