I agree, don't try this at home! I would say a strong stripping agent like Effasol would be best, but not all hairdressers do it. i went from black to red and it took time, and my hair wasn't the greatest colour for a while.
I think most hairdressers charge around £20-£25 per 'strip' and will usually do a maximum of 3 strips in one day. Be prepared for your hair to go a horrible brassy orange (though they should be able to put a toner on for you) and give it plenty of TLC with an intensive conditioner twice a week to stop it going like straw