I had a co-worker who rented a small office, close to his home. Because he lives far away from any larger towns he was able to rent an office for $200 per month, but he shares the space with his partner who also works from "home", so it's effectively $100 per person. Our employer paid for the office space, but not for the cleaning, because it was still cheaper than paying for him being at the office every day (we where short on space).

Depending on where you live, and your living situation renting a small office can be really cheap. In my local area I've seen private office rent for as little as $120 per month, but around $200 is more realistic.