This might be what you are looking for, a '58 Seamaster 420 (manual), all original, in good running condition. I almost bought it myself. I have had a very nice correspondence with the seller (it's her father's watch) and it all seems above-board--comes with the original receipt and customs papers, a rarity! There's even a story about the family in Carlisle paper (apparently they gave their dog a massive operation to save him, 'cause they loved him so much). All of which is to say, an honest seller who is looking for a good home for a decent piece. The price isn't a massive deal, but it's not bad, and it's at the low end of what you were looking to spend. Here's a link to the ad:
http://www.gumtree.com/p/for-sale/gents-omega-seamaster-watch-1958/1073689954
And I attach the pictures she sent me , which I don't think does the watch justice, but will have to suffice. The watch itself was also discussed on the advice thread--just look under '58 seamaster and you'll find it.
View attachment 68784
View attachment 68785
View attachment 68786
View attachment 68787
View attachment 68788
View attachment 68789
View attachment 68790
View attachment 68791
View attachment 68792
View attachment 68793
Click to expand...