[lord2kim]

metlick,

function recalc()
 {
var sum = price_format(parseFloat(document.getElementById('field1').value) * parseFloat(document.getElementById('field2').value));
switch (true) {
    case sum > 0 && sum <= 100:  document.getElementById('fieldRes').innerHTML = sum;
break;
    case sum > 100 && sum <= 200:  document.getElementById('fieldRes').innerHTML = sum - (sum * 5 / 100);
break;
    case sum > 200 && sum <= 300:  document.getElementById('fieldRes').innerHTML = sum - (sum * 10 / 100);
break;
}
 }

где 5, 10 - проценты