Sumar, unfortunately most digs actually expect you to pay them....many years ago you could expect to be paid subsistence but the increased popularity of archaeology has made directors realise how few diggers they actually need t pay. However, many digs will provide basic food or accommodation.
Get hold of a copy of Current Archaeology and /or British Archaeology - you should get lots of leads in there - plus the Institute of Archaeology in London used to issue a summary of digs abroad looking for volunteers.