[exzibit]

function getResult(){
var table= {
		1:{price:350,density:1630},
		2:{price:650,density:1580},
		3:{price:700,density:1620},

		};
var price=0,value=0;

if (measure.value==1) {
		price=((table[product.value].price*count.value).toFixed(2));
		value=((table[product.value].density*count.value).toFixed(0));
		result.innerHTML=price+' руб. ('+value+' кг.)'
	}
else if (measure.value==2) {
	price=((count.value/table[product.value].density*table[product.value].price).toFixed(2));
	value=((count.value/table[product.value].density).toFixed(1));
	result.innerHTML=price+' руб. ('+value+' м3.) '
	}
}

<form onsubmit="return false;" oninput="getResult()">
    <select size=1 id=product  onChange="getResult()">
		<option value=1 selected>Песок</option>
		<option value=2>Гравий</option>
		<option value=3>Щебень</option>

	</select>кол-во:
    <input id="count" type="number" value=1 min=0 oninput="getResult()">
    <select size=1 id="measure" onChange="getResult()">
        <option value=1  selected>м3</option>
        <option value=2>кг</option>
    </select>
	
	Цена: <span id="result">350 руб. (1300 кг.)</span>
</form>

html форма никак не обрабатывается експлорером