I'm trying to create a formula that will identify the relevant commission payment from a long list of sales figures.

I have an established non-linear commission structure:
Sales between:
$0:$499 = $0 in commission
$500:$999 = $75 in commission
$1000:$1499 = $150 in commission
$1500:$1999 = $200 in commission
$2000:$3499 = $350 in commission
$3500 = $650
*sales exceeding $3500 receive $650 and 5% commission on all sales over $3500.

I have tried looking on multiple forums, but nothing seems to work... does anyone have any ideas?

Thanks in advance