Use the pro search or ask for referals from friends or neighbors and get three prices, its hard to tell you something like this as this site is worldwide and prices change based on location.

Kenyon is correct. It depends on where you are, what type of travertine floor, what has to be done to the substrate to get ready for the tile, etc.

It depends. Sometimes backer board should not be used and mud should be.The floor needs to be level and have no lose movement with the floor joist. It depends also on how it's laided and diagonal, straight, etc. How many cuts etc. Get a few estimates and go with the person who will do it right. My exhusband was a tile setter. He did work in some very upscale homes and stars. He had to give it up from his chrons. You don't want cracked tiles. If the grout is not cleaned off right it can stains and then they need muratic acid to clean it off. You want a professional. It's not easy to redo and can be very costly.

Location is the single greatest decider for labour. In Canada, we have several price points because of location. A floor laid in Vancouver BC = $4-$6/sf + extra costs for materials. The same floor in Edmonton Alberta = $8-$12/sf. Toronto ON = $6-$12/sf; etc etc etc.

Start looking for professionals closest to you using the BBB. Each state/province has flooring associations with a list of reputable companies. Start with the TOP and then work down to a middle price. The highest priced can also be a bit of a scam; the lowest price is going to leave you with problems. Middle of the road estimates (with EVERYTHING included) are often just right.