Hi Stanley and welcome. Prices will vary from about 4 dollars per ft to 10 dollars. The travertine will be at least a dollar or two more. There is no set price, you get what you pay for. Be careful.
How many sq ft do you have to install? This will affect the price too.
You need to check your sub-floor with the deflecto up in the top right of this page, it needs to be strong for travertine.