Lol...I've never changed one and I know this...it would still easily take me a day though..
Plus if your mechanic is nice enough to only charge you trade price for parts, some are but many arent, Id say he is quite easily making a couple hundred off this..still a pretty good deal ..many say you should change your waterpump as well but if your radiator fluid is in good nick IE still bright green and not full of rust scale and your water system is clean I wouldnt worry to much about it..maybe Just throw a bottle of radiator flush in before you drive it to the mechanic and drive slowly, or get him to do it...