cheapest would be plywood. Best I will still go with glass over acrylic. Glass is tougher on scratches and there are some more expensive ones that can be as clear as acrylic.
I agree, plywood is the cheapest. I personally like glass, but I know some people like acrylic. Acrylic is more expensive, but it's lighter and usually clearer a little bit. Acrylic is also more expensive...
take a look at some ideas other people had áround this DIY section... i'm sure you will have your own idea based on something you find best suited for you
plywood is cheaper rather than common glass aquarium.
but it depend on you, wanna portable or fix aquarium..
1)fix (extra large)
concrete type ---> ask johnptc as well..
indoor pond type ---> D.I.Y forums helps..
2)portable (large)
plywood --->bigger size easier to move rather than common aquarium
common aquarium ---> ask local aquarium store/local glass store
actually your aquarium depend on the "resident"
wanna paiche?
don't worry, all MFK's will help your out..
cannot wait to see your complete setup.
Good LucK...