You'll get a second hand Tag auto (probably a Link or Kirium?) at the top end of your budget if you shop around a bit, but I think the Tissot PRX Powermatic 80 takes some beating! I had the green dial one and its one of the best watches I've owned in ages. RRP is just shy of £700 but they are in lots of sales at almost exactly £500 at the moment.
Edit. Even better as I see he doesn't like huge watches, the 35mm model is reduced even further on beaverbrooks to £450.