Help with commission formula

Hi - I'm completely stumped with this - I am trying to work out a formula for the following commission scheme:

£ 0-1999 - 0 commission
£ 2000-2001 - 2.5% commission (ie. flat £50 bonus)
£ 2001-3000 - 4% commission
£ 3001-4000 - 6% commission
£ 4001-5000 - 7% commission
£ 5001-6000 - 8% commission

The figure I'm using as an example is £3576.01 and the commission payable should be £ 124.56. All of the formulas I've tried give me the wrong answer as they are putting 4% commission on the whole amount, and it should be 2.5% on the first £2000, 4% on the next £1000, and 6% on £576.01 etc. I have tried a SUMPRODUCT formula, a MAX formula (which gets the closest answer) and a LOOKUP formula.

Thanks!