Hi,
You are correct to NOT give your pictures away to the magazine for free. Even though print publishing budgets are not what they once were, they do still pay. You just have to figure out how much. You do that by asking how they will be running it (cover, inside, size), what is their circulation, will it be used on the web as well. There are calculators that can help you figure out the price you should charge. You could also join the ASMP Pro Advice group (which is an open Yahoo group) and pose the question there, with all the info about the magazine (minus their name), you'll likely get a good ballpark there.
You also want to request that they run your photo credit with your copyright notice. AND when you send them your image you send it with a delivery memo that states that they are buying one-time usage, and that any reuse in the future will need to be negotiated then.
Good luck!