Yes it is.
Get Emerald at gamestop or get Sapphire on ebay.
Its not just Pokémon games- I went to a GameStop here a few days ago and found Final Fantasy X for $9.99 used. I go back about a week later and find it again, now for $16.99. Bad move in my opinion- with the economy in the shape its in, the last thing GameStop needs to do is raise prices for games.
But yeah, Pokémon games are still expensive. If I were you, I'd see about getting a new copy, since a used runs a chance of not working.