[Deff]

ireznik,
Замените На такой:

<style type="text/css">
div.disabled #search_params_attributes_return_date{
 background: #D3D3D3!important;
}
div.checker#uniform-aviasales_one_way_checkbox span.checked{
 background: url("http://ireznik.com/sprite-6.png") no-repeat -38px -260px!important;
}
div.checker#uniform-aviasales_one_way_checkbox span{
 background: url("http://ireznik.com/sprite-6.png") no-repeat -114px -260px!important;
}
</style>
<script>
window.onload = function () {
setTimeout(function(){//
  var a=$("#aviasales_one_way_checkbox")
  a.click();
  var a=$("#search_params_attributes_return_date");
  a.attr("disabled","disabled");
  a.parent().addClass("disabled")
},200);
}
</script>