Notice the lack of quality advice you are getting. Nothing wrong with the people posting. It's just that they have ZERO information to go in except price. Did you even specify if you were looking foe a digital SRL or a Film based SLR?
Given your budget, you will be buying used gear. You will find out quickly that most used gear on the market is Nikon and Canon
The very first thing you need to do is understand and then decide on a lens. Lens make images, the SLR body only captures that image. With a low budget look for an older SLR body. Something like a Nikon D50 would be great and would sell for about $300 or less. This leaves more budget for a better lens.
First pick a brand. The way to do this is to read ads for used lenses. If you pick Nikon then every lens you buy will be a Nikon Lens and over time your collection of them will be worth a LOT more than the price of the SLR body. S lelt the availability and price of lenses guide the brand selection. Look at flashes too. These are surprisingly expensive and complex. The SLR body is the lost price part of a modest system. Try and guess what what equipment you will want over a five year period
Next post here more information. Without it all the advice you will get is "I have XX buy an XX" which is not helpful unless your needs are like his needs. You might say how and when you will use the camera. The types of photos you want to take and what you do with them. Lastly WHY do you want an SLR, there are good reasons but why do YOU want one. Are there subjects you can't get with the current camera?