For 5 pairs at $100, I would have immediately picked them up. Even iff the other speakers are garbage, you should be able to sell them for at least $20 a pair, if not more, if they are working.
I've made many pickups where I buy a package deal, but I only want one thing. Usually, that one thing is worth the package price. The extra stuff just takes up space until I can get rid of it. Oftentimes I get what I really wanted for free. For example, Someone was selling his whole system for $100. The system included Polk bookcase speakers, Polk tower speakers that I quickly sold for $100, a tape deck I resold for $30, a CD player I resold for $35. I got the receiver that I wanted and had a pair of Polk bookcase speakers, and I made $65. So basically, the seller paid me to take his stuff away.