A $20 Timex will probably keep better time than a $2,000 Omega. The reason for this is that almost all watches under $500 use quartz movements, which are cheap to produce and are highly accurate with a typical deviation rate of less than +/- 20 seconds a month.
Mechanical movements, such as automatics, are generally the domain of more premium watches. They are inherently more complicated and expensive to produce and will not tell better time than a quartz watch. The standard deviation rate for a mechanical watch can easily approach +/- 20 seconds a day. This is difficult thing for many watch purchasers to accept as they falsely, with good reason, expect a strong correlation between price and timekeeping performance.
But don't despair: a mechanical watch arguably represents the highest form of hand-crafted engineering and art. There is no comparison between a finely crafted mechanical Swiss watch and a cheap quartz alternative in terms of fit and finish, materials, craftsmanship, design, and so on.At a certain point, however, mechanical watches become more expensive not for these characteristics so much as because they are built with fine metals (platinum, gold) and jewels (diamonds). In effect, you are paying for a piece of jewelry as much as you are paying for a fine watch.