I think £500 per day is cheap, it depends on your skill set etc what you can demand.
I charge consultants out where i work between £1k - £1.5k per day. Friends of mine are software consultants and wont get out of bed for less than £700-£900 per day and that is just a normal work day - for weekends they would charge 1.5 - 2x normal rates for Xmas weekend 3x minimum.
As an aside I think the term 'consultant' is over used and primarily by Support Engineers.
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