Roomster 1.4 tdi intermittent brake binding rear near side disc

I have a 2007 roomster tdi 1.4, the rear near side brake seems to be binding when I use the brake. It does not happen every time the brake is used and also releases its-self if I tap the brake again. My local garage says I need to change the caliper and disc, even though at first they said it carnt be a caliper fault due to binding being intermittent. I have been quoted £400 for labour caliper disc and pads is this a reasonable amount to pay.