[kuzkuz]

Ну как то так наверно, измени под себя и будет тебе счастье:

function calc() {
		    var rating = document.getElementById("rating");
		    var plan = document.getElementById("plan"); 			
            var result = document.getElementById("result"); 
            var price = 0;
			var cash_frend = 3000;
			var bonus = 25000;
			var oklad = document.getElementById("oklad");

			var drug = document.getElementById("drug");
			var bon = document.getElementById("bon");
			var cash_bonus = document.getElementById("cash_bonus");

			var ok_mont = document.getElementById("ok_mont");
			var month = document.getElementById("month");
			var overtime = document.getElementById("overtime");
			var over_price = 200;
			
			price += parseInt(rating.options[rating.selectedIndex].value);
			price += parseInt(plan.options[plan.selectedIndex].value);
            price += parseInt(friend.value) * cash_frend;
			price += parseFloat(mesto.value) * bonus;
			price += parseFloat(over.value) * over_price;
				
			
            result.innerHTML = price;

}