If Payplan say that they will act for you on this basis then this is a good place to start. Another good company to call is ClearDebt who have a good reputation for proposing and getting IVAs accepted at a lower level of disposable income.
Go for it - if Payplan say they can do it then you should be ok.
As Mel says, Cleardebt are another firm who take on low payment IVAs.
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk