It's true, that many volunteer opportunities for archaeological excavations are set in exotic places and meant in part as a holiday for people rather than a training session. Under those situations, you will probably need to pay tuition or volunteer fees in addition to travel, food, and housing. But, fortunately, there are loads of archaeology clubs around the world, and some of them have made deals with universities conducting local excavations to have training days, where the membership may spend a couple of days or a week at a nearby excavation for a nominal fee. So my suggestion to you is to find a local archaeology organization and ask them if they do that sort of thing, or know of an opportunity that might come up next field season.
Here are some links to get you started:
- Finding the Right Archaeology Club for Volunteers, which describes what you should look for in a club
- Smoke Pfeiffer's Directory of Archaeology Associations, which has a list of professional and amateur archaeological associations in the US, Canada, and Australia
- Current Archaeology Digs, which lists many of the upcoming and ongoing archaeological digs around the world
