Do a search, btw there's no right answer. You are worth what someone is willing to pay...
I've seen salaries for an employed developer range from £15 - 80k a year. (the majority earn between 20-30k though)
When I was freelancing I charged per job, but I always made the mistake of undercharging, the client would make the scope creep and I ended up earning fuck all and working all the time. Actually, not much has changed now I'm employed.
