They are benefiting from this just as much as you are. Remind your employer that he's also saving money by not having to pay for an expensive office space in the city center and all the things that go with it like hiring cleaning services or building staff. Any equipment you use to work on should be either reimbursed by him or factored into your salary as well (monitor, laptop, internet connection, office chair, desk, etc). There are a lot of bargaining chips, just depends on how you present them.