JSFiddle - React, Tailwind, and code Playground

HTML

<select>
        <optgroup label="prima scelta">
            <option value="#">---scegli---</option>
            <option value="1">1 opzione € 1.00</option>
            <option value="2">2 opzione € 2.00</option>
            <option value="3">3 opzione € 3.00</option>
        </optgroup>
        <optgroup label="seconda scelta">
            <option value="4">4 opzione € 4.00</option>
            <option value="5">5 opzione € 5.00</option>
            <option value="6">6 opzione € 6.00</option>
        </optgroup>
    </select><br>
    
    
    
        <input type="radio" name="primoradio" value="+2" > <strong>scelta radio1</strong><br>
        <input type="radio" name="primoradio" value="-2"> <strong>scelta radio2</strong><br>
            
       <input type="radio" name="primoradio" value="0"> <strong>scelta radio3</strong><br>

    
    <input type='text' name='totale' value='€ 0.00' disabled>
</form>

JavaScript

$('select').change(function(){
      		var add = parseInt($(this).find('option:selected').attr('value'));
            var check = parseInt($('input[name=primoradio]:checked').val());
         if(!isNaN(check))   add += check;
    		$('input[name=totale]').val('€ '+add.toFixed(2));
		});
		
$('input[name=primoradio]').change(function(){
            var v = parseInt($('select option:selected').attr('value'));   		    
                $('input[name=totale]').val('€ '+                                       ((isNaN(v)?0:v)+parseInt($(this).val())).toFixed(2));
		});