This idiom traces back to a time when a dime, a small coin, could buy a dozen of some cheap, mass produced item, which made the phrase a natural way to describe anything so abundant that it holds little special worth. Over time it stopped being about literal pricing and became a general expression for things, or even people, that are extremely common and easy to come across.
Options 1 and 2 stay stuck on the literal transaction, treating the phrase as if it were describing an actual sale of a dozen items for a dime, missing the figurative shift the idiom has undergone. Option 4 gets the meaning backwards, suggesting scarcity, while the idiom is really about the opposite, an oversupply of something so that it is easy, not hard, to obtain.
Understood figuratively, the phrase describes something common and readily available, so the correct answer is option 3.