You're making this harder than it needs to be. Your tenant market isn't "freelancers," it's "freelancers who can afford $x/month." You just need to decide how much "x" is based on the desirability of the space.

Basing rent on what it costs you to service the place is OK if you just want to keep the space occupied, but not if you intend to make money. So make the decision: which is it? Profit or occupancy?

I was a landlord for a few years and had to deal with this every time a lease expired; it isn't rocket science.