Hello Lucas, Welcome to PR...I'm not sure how much we can help you. There are a few DSLR's available in the $600USD range. I use the Pentax *ist DL with some practice it would work for you, however, it is a little slow, but does have the 2.5 frames per sec. The E300 has been recently upgraded to the E 330. and the E 500 is also a nice camera. At this price then there is the Canon Rebel. A bit higher in price. The biggest problem is that these cameras are a little slow compared to the higher end cameras.
I do have a question. What camera have you been using, the Olympus?, and what lenses do you already have. This could make a big difference on what you can afford and would give us a better idea what to recommend.
Ken