Schiphol has a 7x24 luggage depot, in between Arrivals 1 and 2. Don't know how much they are charging. You may want to check the latest information on the Schiphol website, try a search for: heavy luggage. I think this is your best bet, but you'll have to travel back and forth from Amsterdam to Schiphol, unless your train has a stop at Schiphol.
Amsterdam Centraal only has automatic luggage lockers. You may also want to check out "Lock", Luggage Storage Amsterdam, but it is a little under 10 minutes walk from the station.
There are storage places like http://dropandgo.nl/ across from the station but they charge per bag. Might be an option if the lockers at the station are full.
Thank you very much!