The 2005 Mazda Tribute had either a 2.3-litre four-cylinder engine or a 3.0-litre V6, both of which had timing chains. They don't normally require changing. The only reason you might change the chain was if it was worn and/or noisy. If it's a 2.3-litre four-cylinder engine it's likely to cost around $2000, if it's a V6 it's going to be closer to $3500.