Bulk seed is donated as individuals operating SPI have long relationships in the seed industry. Only seed with good viability is accepted and many current industry varieties are donated. 

A large paper company donates the paper sheets used for printing seed packets.  A company in New York prints the packets at low cost.  A packet seed company in East Rochester, NY performs the following functions at low cost - warehouses seed, keeps track of inventory, fills packets with seed, places packets in protective plastic bags, loads pallets, arranges for Phytosanitary Certificates, and loads trucks. 

Two private, accredited seed laboratories test for germination twice a year at no cost. 

FedEx Trade Networks (JFK) provides freight forwarding services at low cost. 

We do pay needed suppliers, but they charge us low cost because we are a humanitarian organization helping the poor and hungry of the world.