dorrough

I've lost one of the master keys to my 2004 Sienna minivan. I can buy a blank key, but it costs quite a lot to have it programmed. Programming seems to be a matter of inserting a working master key, they putting in the new blank key and following a series of steps (open doors, press pedals, etc.) Does anyone know how to program a blank key, so I can do it myself? I'm hoping to avoid paying $500 for a new key if I lose this last one. I can buy a blank key for about $30, and get it cut for almost nothing, but I don't know how to program it. Thanks for any advice ...