Actually, you can't use one-piece cranks with that frame, because it uses a Euro bottom bracket as opposed to an American (the Euro BB has a smaller diameter than the American - not large enough for a one-piece to fit through).
That's too bad, really, because to get new three-piece cranks (which would cost more than half of what that bike costs), you'd also need to get a new sprocket, because the Redline cranks have a built-in spider with a bolt-on chainring.
Sorry.