Piano info!

[VenalWinfrey]

Does anyone know what the average rate of pay would be for a free lance pianist? I have recently changed careers (for the better) and am now pursuing my dream of being a solo pianist. I have managed to negotiate a couple of contracts - one of them is with a hotel, the other with a bar in London. Both are well established venues in the West End. I would not wish to say more. My concern is that I am being significantly underpaid. For one I perform on an ad hoc basis as and when required. For the other I do a regular set of nights per week, each set two hours long, non-stop. I used to do this work three years ago but stopped. The current bar, on hiring me, were just starting out with the idea of a piano, and assured me that they knew they were underpaying, but that they would review it if the idea were successful. It has now been six months, it is proving a success, yet they (of course) have not approached me with the prospect of a pay review. I am thus now writing a formal letter to request this. But I really do not know what to expect. Does anybody either know roughly what a reasonable rate of pay would be, per hour/night etc. for a professional solo pianist? I have a music degree, two grade eight distinctions, and have been studying from the age of six. I am now thirty, have much performing experience and thus believe I am due for consideration of a review. If anybody could point me in the right direction (i.e. a website specialising in this kind of thing - I know there is a large pay range in music), or suggest a figure, that would be much appreciated.
As an indicator, the rate I was being paid 3yrs ago was more than triple what I am currently receiving. Whilst I really neeeded the current contract that I took, I am now in a much better position, and would thus like to consider pursuing other contracts/venues, but do not know what roughly I should set out to charge. Thanks everyone for reading, and any suggestions greatly appreciated