Breeders think in terms of "breeder's space."
They don't give their animals much space because space costs money, and breeders make more money by housing their animals in the smallest space possible without the animals dying right away.
You can't give a turtle too much space... at least for the turtle. It may turn out to be too much space as far as you are concerned because the turtle hides so well!
The spotted turtles being so small actually would present a different problem to you... how to feed them. Baby turtles are harder to feed than bigger ones.
But there are adult spotteds for sale if you just look. They are a great turtle, merely expensive. They don't get too big, they're very smart and friendly, and they tolerate cooler tempertures than tropical turtles.
I'd pick them over a R.E.S. every time.