A question on the tenants wanting a lower price; have you reviewed who these tenants are? Just because the agent found someone, doesn't mean you have to jump at it. You should also review who these people are on paper.
If it was me, I would want a mature couple or young family. Not a single guy who may have a party every weekend and have your place trashed.
Go 500 for 6 months or 12 montsh with 520 rise after 6 months like other have said.