Your budget is tight but feasible -- don't forget that you will probably want a memory card of some stripe to go with the camera itself. We bought my stepdad-in-law one of these (http://www.jessops.com/Store/s31463/0/Digital-Compact-Cameras/Kodak/Easyshare-C310-Digital-Camera/details.aspx?&IsSearch=y&pageindex=1&CatId=236&comp=y) for Christmas and he seems to find it fairly easy to use -- the site suggests it'll work with a Mac and also with a PC but I can't offer you any first-hand advice about the Mac end of things.

As to where you go to get one, well, Jessops are good, larger Tescos seem to be selling them these days (well, the big one near us does), and so would PC World and the like. I have no idea which, if any, of those exist near you, sorry ;)