The first thing to do is to decide what style of watch you like, you can do this by looking at watches from different decades, as they are quite distinctive, although many styles do cross over the decades. A good place to start is with the what are you wearing thread, this will show you many styles of watches. If you want an omega watch then you could also type in the different model names, deVille, Seamaster,Speedmaster, Geneve and Constellation, this will also give you an idea of the different looks of Omega watches, although there are many. You then should decide if you want vintage or modern.
Basically there are mechanical watches, quartz watches, and automatic watches, which are self winding as long as you are wearing them. The f300 and megahertz are excellent watches although many collectors are not interested, probably because they are considered technical innovations rather than horological innovations. Quartz watches were made by Rolex, Patek Philippe and Omega and are top quality watches.
There are plenty of options for your budget, but obviously dealers will be looking for a decent profit. You can check watchrecon, chrono24 and ebay. The main thing is to make sure you are getting what you think you are paying for which is why it is worth checking here first. By not rushing into anything,you will find what you are lookng for, and you will get it for a reasonable price.
