Your budget doesn't leave a lot to work with if you want a four stroke.
Let me start by explaining that the major manufacturers offer dirt bikes in two basic catagories: "Off road" and "MX".
MX bikes are built for racing. They have high performance engines (high compression) which require premium gasoline and can be significantly harder to start and a bit more tempermental. They are kept as light as possible, so you aren't going to find a factory kickstand on a MX bike (and kickstands are not allowed in many races, they don't want it to fly off during the race). On the plus side, they will have better suspension and generally be a more rugged frame.
The "off road" bikes are built more for the average guy who doesn't want to race. The seat height will often be a bit lower, which is better for shorter people (doesn't look like that would me much of an issue for you). Kickstands are fairly standard feature. Newer models come with electric start. Usually four stroke models. They are also significantly cheaper.
To get into your price range in a four stroke I believe that you will need to get an "off road" bike that is 5 years old. This is fine, as a beginner it is actually a more appropriate bike for you. To get a MX bike in your price range you would need to go 10 years or older and it wouldn't be in as good a shape.
What you want is something in the 225cc or above, anything less in a four stroke would be too small. A Yamaha TTR-230 would be a good choice.
Rod