I've obtained cranks from the local dump (ok, transfer station) for free. I've had to take the complete bike on occasion, but you can't beat free. These have been for regular bike rebuilds, not motorized bikes, but the principle still applies.
And if you paint that thing, take detailed photos of it first, then paint it like it originally was painted.
And if you paint that thing, take detailed photos of it first, then paint it like it originally was painted.