Well heres an adult size one that is 50 oz for 26 dollars.

http://www.jensonusa.com/store/produ...drobak+06.aspx

another 50 oz which is 40 dollars

http://www.jensonusa.com/store/produ...Stream+06.aspx

70 oz for 40

http://www.jensonusa.com/store/produ...lassic+06.aspx

I mean for 40 you have tons of choices other than the kids model.

Or like I said you can buy any cheap pack from anywhere. and use a 100 oz insert

http://www.jensonusa.com/store/produ...ervoir+06.aspx