you can use Jquery selector like "ID ends with":-
$("[id$='txt_insurance']")
above statement fetch the element whose ID ends with "txt_insurance".
for an example :-
var eleid=$("[id$='txt_insurance']").attr('id');
var rep=eleid.replace("txt_", "val_");
alert(rep);
$("[id$='txt_insurance']").attr('id',rep);
//this will replace old ID with new which is 'ctl00_MainContent_val_insurance'
UPDATE:-
var ele=eleid.split("_");
alert(ele[ele.length-2]+'_'+ele[ele.length-1]);
var originalid=ele[ele.length-2]+'_'+ele[ele.length-1];
// originalid will give you original id of element :-
so you can proceed like :-
$('.myform :input').each(function ()
{
var id = this.id;
var orgid=id.split("_");
var orgid1=orgid[orgid.length-2]+'_'+orgid[orgid.length-1];
var id2 = $("[id$=" + orgid1 + "]");
});