if you get a cage for a full size adult frilled, you won't have to worry about spending more as your frillie gets older... also, i'm not sure about the waterfall, but that's a really good idea, i'll be checking back to see the responses you get from this so my brother can decide if he wants one or not 
take care! sorry i couldn't be of much assistance to you 
[aimee]
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1.0 Albino Leopard Gecko (Melvin)
1.0 Black Lab / Pitbull mix (Mikey)
1.0 Blue Fighting Fish (Blue Balls)
1.0.1 Fire-Bellied Toads (Norman & Forman)
http://aimee.i8.com