As BillD said, Cost effective no.
I would consider it if I wanted a custom size.
If you would be happy with a standard sized aquarium then used is the best deal out there. And I might add 29gallon tanks can be had for free or practicly free sometimes.
custom, there are custom tank builders in canada and the US, if you want a custom you might want to look these guys up and see how much they are charging before putting your plans together for building your own tank. your time is worth money, how much is up to the individual (depending on your income and or the type of work you do the time put into such a project will have to be for fun otherwise this could be very costly)
now that thats over. the plans here used to point to http://garf.org/tank/buildtank.asp