I would be very wary of anyone that wants that ammount of money in advance.
Take a look at www.iva.com there you will find a list of IVA Providers and reviews on each.
Please take advice from 2 or 3 companies to be sure ALL options are discussed fully with you.
There is no need to be wary about paying money over to an Insolvency Practitioner - but do your homework and make sure that it is going to be held on a properly designated client account to be returned in the event that the IVA is not accepted.
I would often ask for third party monies to be lodged prior to the creditors meeting, as this conveys that there will be an immediate return to creditors.
Is the money available to be paid over now, or are you just wary of doing this?