Of course its a scam. They are asking you for money. You are trying to find work and you are being asked for money. Red Flag there! Just imagine going on a job interview and the interviewer says "we'd like to offer you a manager position here in our warehouse, but we are going to have to charge you $50 for the privilige". You would get up and walk up!!!
Envelope stuffing is one of the oldest cons around! No one pays big bucks for someone to stuff envelopes. A company can either pay a local and/or temp minimum wage or for just a few hundred dollars, they can get an envelope stuffing machine that will stuff the envelope, address them, seal them and put on the postage and sort them.