quite complicated functions(ebay fees)

hi there.
what i want to do is create a spreadsheet to work out how much i would need to sell an item for on ebay.

sold between £0.01 - £4.99 10% for the amount of the selling price up to £4.99
£5.00 - £9.99 - 10% for the initial £4.99 plus 8% of the remaining selling price balance
£10.00 - £49.99 - 10% of the initial £4.99 plus 8% of the initial £5.00 - £9.99 plus 6% of the remaining selling price balance
£50.00 - £499.99 - 10% of the initial £4.99 plus 8% of the initial £5.00 - £9.99 plus 6% of the initial £10.00 - £49.99 plus 4% of the remaining selling price balance

right.
so if i sell an item for £40 i need to be able to see how much i would pay in fees
any idea how i could do this? i did some excel functions at GCSE level but not many and i have tried and failed with this once i know the function i can work out some of the other stuff i need myself. just that first bit would be nice.

cheers