Contact your local USA Boxing (governing body for amateur boxing in the USA) rep to find out about gyms/coaches in your area.
There was an Irish Boxer called Wayne McCullough who won a silver medal in the 1992 Olympics. He turned pro the following year in the USA. He came back to this part of the world quite a lot.
He said in the USA, some gyms train pros and amateurs together. A good example of this is Gleasons Gym in New York. Gyms like this are probably going to cost more, as coaches are more likely to be professional, plus they have the added overheads of running a gym full time.
Amateur clubs tend to train a few nights a week or at the weekends. They are usually pretty inexpensive. Amateur clubs are great places to learn the fundamentals of boxing. Although it is fair to say the rules of amateur boxing and pro boxing are different, the basics of boxing are the same.
I would look for a USA Boxing approved gym if I were you.