I get people in the store all the time wanting to buy turtles, since at about $15 they look like cheap pets.
But since (in the USA) its illegal to sell turtles smaller than 4 inches, these are good sized turtles.
We generally recommend at least a 40g breeder tank for this size, with a bigger tank (or a whole room!) for them when they grow (remember, this pet may be around 20-30 years or more).
Generally, a basic aquatic turtle setup at our store (UV a/b lighting, basking light, filter, tank, stand, screen top, etc) is probably about $300-400.
For a land turtle (tortis) it is usually a little cheaper, maybe $200-300.
Plus the tortises tend to foster much lower bacterial counts (not living in such a hot wet environment) so they are generally much better pets for homes with children.
(we also get a ton of customers in who bought the "illegal" tiny turtles at the local flea market (etc) - they always come in with no idea what the turtle truly needs, and are generally told that they can keep it in a #$%^ plastic shoebox ! )
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