This is the tank I use to house one or at most, two adult mud turtles in. It is not set up for breeding but is a maintenance aquarium only.
Maybe it is because we have some large aquarium stores down here but these are easy to get tanks that are not that expensive. Fifty-five gallon tanks are very cheap though since they are the most common (besides ten gallon) size.
If I am not mistaken, the forty breeder tank is the same as a fifty-five except that the forty gallon is not as tall.....four inches shorter I think??
BTW, this is a pretty basic set up and it could be nicer.