If there is any way you can double check that it works, you should. Some 32x's and Genesis consoles will not work without the two silver attachments that hold down the cart flap and from past experience (ie everyone always loses those pieces) I'm sure those aren't included in the package you saw. Then again, about 80% of 32x's and Genesis consoles will work without the silver things. Mine won't, though (luckilly I bought my 32x new so I still have the silver attachments).
$20.00 seems like a reasonable price though, just try your hardest to test it out before buying.