или с JavaScript, както са го направили тези от примера
function calculate(){
if (document.calculateValue.designer[0].checked){
var designer = 'you';
}
if (document.calculateValue.designer[1].checked){
var designer = 'puremaestro';
}
var roomSize = document.getElementById('roomSize').value;
var reg1 = new RegExp('^([0-9]*)[.]([0-9]*)$');
var reg2 = new RegExp('^([0-9]*)$');
if ((reg1.test(roomSize) == false) && (reg2.test(roomSize) == false)){
alert('Внимание въвели Ñте забранен Ñимвол!');
document.getElementById('roomSize').value = '';
}
else{
if(designer == 'you'){
if((roomSize>0) && (roomSize <42)){ var price = 650;}
if((roomSize>41) && (roomSize <62)){ var price = 810;}
if((roomSize>61) && (roomSize <100)){ var price = 1000;}
if((roomSize>99) && (roomSize <139)){ var price = 1260;}
if(roomSize>140){
alert('За Ð¿Ð¾Ð¼ÐµÑ‰ÐµÐ½Ð¸Ñ Ñ Ñ€Ð°Ð·Ð¼ÐµÑ€ над 140 кв.м. цената е по договарÑне');
document.getElementById('roomSize').value = '';
document.getElementById('price').innerHTML = '0.00';
die;}
}
if(designer == 'puremaestro'){
if((roomSize>0) && (roomSize <42)){ var price = 910;}
if((roomSize>41) && (roomSize <62)){ var price = 1134;}
if((roomSize>61) && (roomSize <100)){ var price = 1400;}
if((roomSize>99) && (roomSize <139)){ var price = 1764;}
if(roomSize>140){
alert('За Ð¿Ð¾Ð¼ÐµÑ‰ÐµÐ½Ð¸Ñ Ñ Ñ€Ð°Ð·Ð¼ÐµÑ€ над 140 кв.м. цената е по договарÑне');
document.getElementById('roomSize').value = '';
document.getElementById('price').innerHTML = '0.00';
die;}
}
if (price == undefined){
document.getElementById('price').innerHTML = '0.00';
die();}
document.getElementById('price').innerHTML = price;
}