<form role="form" action="catalog/vse-tovaryi/">
<select name="ms|price">
<option value="">Любая</option>
<option value="500">500 рублей</option>
</select>
<select name="msoption|tags">
<option value="1">Тэг 1</option>
<option value="2">Тэг 2</option>
</select>
<button type="submit">Подобрать</button>
</form>
<form role="form" id="form" action="catalog/vse-tovaryi/" data-def="catalog/vse-tovaryi/">
<select name="ms|price">
<option value="">Любая</option>
<option value="500">500 рублей</option>
</select>
<select name="msoption|tags">
<option value="1">Тэг 1</option>
<option value="2">Тэг 2</option>
</select>
<button type="submit">Подобрать</button>
</form>
window.onload = function () {
var form = $('#form'), def = form.data('def'), data = {}, action;
$(document).on('change', '#form select', function () {
var el = $(this), val = el.val(), name = el.attr('name');
if (val) {
data[name] = val;
} else {
delete data[name];
}
action = def + "?";
for(var i in data) {
action += i + "=" + data[i] + '&';
}
action = action.substr(0, action.length - 1);
form.attr('action', action);
});
};
<script src="https://code.jquery.com/jquery-2.1.3.js"></script>
<script type="text/javascript">
<!--
$(function(){
$("#sendForm").click(function(){ // При клике по кнопке #sendForm
if ($("#msprice").val() == '') // Если в элементе #msprice выбрана опция с пустым значением
$("#msprice").remove() // Удаляем #msprice с формы
});
});
-->
</script>
<form role="form" action="catalog/vse-tovaryi/">
<select name="ms|price" id="msprice">
<option value="">Любая</option>
<option value="500">500 рублей</option>
</select>
<select name="msoption|tags">
<option value="1">Тэг 1</option>
<option value="2">Тэг 2</option>
</select>
<button type="submit" id="sendForm">Подобрать</button>
</form>