Hi Warren,
You can check your provisional allowances against the Stepchange Budget Guidelines Report here.
https://docs.google.com/file/d/0B7LabJy ... edit?pli=1
(Sorry, have not yet been able to get hold of the latest version that came out in October 2013, but the figures only differ by a couple of quid here and there).
It is well worth a read, as it covers every form of expenditure, right the way down to allowances for hairdressing, kid's school dinners, meals at work, even hobbies etc.
If you are careful to correctly record your income and expenditure, your IVA payment should be set at quite an affordable level.
Well worth a second or third opinion from another company or two, especially as there is a fair chance that will likely refer your IVA to Grant Thornton anyway. (Just google 'Grant Thornton Complaints' or have a look at some of the other forum posts here to see why that may not be in your best interests).
Good luck.
My opinions are just that: Based on my experience and being a self-employed IVA customer.