You won't get a really good embroidery machine for $600 - the cheapest new, embroidery only machine starts at about $800 - then add in your start up costs of stabilizer, thread & needles... you are looking at a good $1000.
You might be able to find one used - and used can sometimes be good - but then it can also be bad. I have sold used machines in the past but my machines do not get any wear and tear on them... other people have machines and they run them hours every day, getting ready for craft shows or selling things online and whatnot - that machine is a bad one and will probably poop out on you quickly. You just don't know what you are going to get - although *some* of the machines have a stitch count on them so you can see how many stitches have been sewn on it....
You might find a used one at a dealer - and that would be a good way to go but you will probably not find one that also sews - when you add the sewing feature to an embroidery machine, the price more than doubles.
You don't really want one that also sews - because trust me when I say that there are a lot of times when you just want to hit start and do something else - there are other projects that you have to stand there and make sure the material isn't going to get sucked in to the machine lol.
If you look long enough though you will find one - but don't be too attached to the must also sew bit. If you have a sewing machine already, use that for sewing and keep the embroidery machine separate ;)