Burdbuster,
A few suggestions for you based on your post. First, see if there are any active retriever clubs in your immediate area or region. Seek to join a club and go to a scheduled event (hunt test). While at a hunt test, try and observe some dogs at the junior, senior, and master hunter stakes. This will give you a good perspective of what levels of training can be achieved by a retriever and his owner / handler / trainer. Do not be afraid to ask questions of and network with club members. Be up front and tell them you are looking to purchase and train a retriever. You will find that these folks are an incredible source of knowledge / information, and great resources for connections to reputable breeders. Once you get a pup, they can help you connect with a training group of the appropriate level, which will be extremely helpful to you as a novice trainer.
Regarding started pups / dogs, I would not expect that you will find any in the budget range you have described ($600). Rembember, "started" is a relative term and means different things to different people. I think you would be better off taking any extra money you might spend on a "started" pup / dog, and putting it toward the purchase of good training literature / CD's such as Evan Graham's Smartwork Series. This coupled with support from club members and a training group should put you on the right track.
Write down what your goals and objectives are for a gundog. Go to watch a hunt test as I suggested. Re-visit your list after going to watch a hunt test and re-identify your goals. Once you have done so, start seeking breeders and tell them what you want in a dog, it may just be a companion and hunting partner, it may eventually include running him in hunt tests. Good breeders can often set you up with a breeding that will throw pups with a inclination toward what you are seeking. Seek breeders with bloodlines that have proven field genetics and not just show stock. Do your homework and ask the right questions specific to health clearances of potential sires and dams.
Once you decide on a breeder / breeding, remember that you might have a schedule in mind for your dog, but dog's do not train according to a schedule, they are individuals and develop at their own rate, given their innate potential. Sometime ago, I was presented with an axiom specific to dog training that I feel is a very wise bit of knowledge, "Make haste, slowly", that is don't rush things that should not be rushed. Most dog training programs present their material in a logical sequence. The sequential order and progression might move faster for some dogs than others. Do not skip steps, make it fun and succession based for you and your dog, and train with specific goals in mind. Goals can be re-visited and changed as training successes are gained. Alway re-visit early fundementals with your pup and continue to reinforce and build on them.
Remember that obedience is the root foundation of all dog training, establish yourself as your dog's pack leader, let him know what is expected, and keep those expectations consistent. Do not rush to hunt with him in your first year at the expense of not establishing solid obedience. It takes self discipline to do this, but you will have a dog that others will envy in the longrun. Good luck with your search and training. Let us know how it goes.
Mike Enright