There is a sadness about empty benches that attacks me

A few hours ago, I sent off an e-mail basically refusing to do a weekends worth of photography work for, once taxes have their way with me, ?150.

No one wants to loose a potential client. But accepting to do work for a price that wouldn't even cover half our monthly electricity bill isn't an option either.

How do I deal with those not valuing my services for what they're worth? Any thoughts?