The payment has to be based upon a fair and reasonable amount that you can afford to repay, there are also other considerations such as whether you are a homeowner, equity, how many creditors and a whole host of other factors.
There are some firms that will not propose an IVA without a minimum contribution in the region of £200, other firms will look at a lower contribution but, again, in reality it has to be based upon your own individual circumstances so it is impossible to answer the question with a definitive figure.
I suggest you may wish to go to
www.iva.com and look at a list of providers and reviews and then contact 2 or 3 people to get a professional opinion.
Good luck.