This is the formula required but when implementing it in Excel (ignoring the 2nd commission with VAT element for now), it does not give the correct result (Note: the cost here includes the postage charge too of 75p):

Price = Cost + Comm + Profit
Price = Cost + Price*Comm% + Profit
Price - Price*Comm% = Cost + Profit
Price * (1 - Comm%) = Cost + Profit
Price = (Cost + Profit) / (1 - Comm%)

Price =(G8+G4)/(1-G9)

e.g:
The Cost = £10.75
Commission = 2%
Profit = £1

The formula needs to give us the selling price (inc vat) = £14.45