I paid 260 notes to get my cam and alternator belts done, but 100 quid sounds cheap. If they are going to do the work get them to change the water pump aswell while they are down there.
I would also get them to do a service using 5w40 semi or fully synthetic oil. Our early dCi 120 suffer from turbo failures caused by wrong oil and Renaults stupidly long 18000 miles service intervals. Get the oil changed and do this every year or 9000 miles

Black 03 Megane dCi 120 Dynamique Sport Hatch. Gone but not forgotten.
Black 56 Pug 207 GT 1.6 Turbo