That highly depends if a collector need it desperately. Then maybe Kuginnii and Cash come together for the Clash of the titans again and fuel ur auction with a nice heavy bidwar.
If they allrdy got the sword (Wich I can't tell you) the price would be around 50e+ cause dual zeal has not the use as a duo vamp and is more or less a pure collection-mod. If they bid war it can go up to 400e xD so post it for auction and pray they both need it and will throw pink globs at u