You will probably see the biggest price range in the color choice. Typically, the colors are in "Levels". Around here, Level I colors are around $48/sq. ft. from a stone subcontractor (no Home Depot installs). Level II is around $52/sq. ft. and Level III is $55/sq. ft.
As a builder, I rarely install anything other than level I. There are plenty of beautiful colors in this price range, so I see no reason to spend more money. A special note - Each supplier determines what colors fall into their price categories. There are a few colors that I use that are Level II and one of my suppliers, but Level I at another.
Another thing I have seen is a change in the thickness. Granite is typically 3cm for kitchens. Some companies are now selling 2cm for kitchens for lower cost. Since granite can break, I see little justification for the minimal savings of 2cm material. Special Note - Watch out for 2cm installation with a "built up" 3cm front edge.
You will also see varying charges for the "extras" The $100 per foot contractor you mention probably doesn't charge for polished sink cutouts or cooktop cutouts or for premium edging. The contractors advertising the lower price per foot may tack on $100 per cutout + polishing and as much as $10 or more per linear foot for the front edge detail.
The last difference, and in my opinion the most important, is how the stone is cut and polished. Many shops use manual labor and hand tools to cut their slabs, polish the surface, and create the edges. The company I use has a million dollar piece of equipment with robotic precision that cuts, polishes, edges, & drills the slab. I have found that I get cleaner lines, better seams, and fewer seams from this company.
The bathrooms could be installed with 2cm material if you chose. They don't take the beating that a kitchen countertop does. However, what I have found is that you can negotiate a better price for vanities from "remnants" that the supplier will have on their yard. I usually get these installed for around $35 per sq. ft. Special Note - the sink can affect the cost. A polished cutout for an undermount sink will probably add at least $100 per bowl. Due to the small quantity, you probably will be better off biting the bullet and installing all the stone together.
The cost of the template is no more than a couple of hundred dollars...unless its done wrong. You don't want that kind of responsibility. Let the stone company make their template and be responsible for the proper shape of the top.
If you bring the bowed wall to the attention of the templater, I would think that he could make the template fit so the stone would follow the wall, bow and all. However, there will still be a gap between the granite and the wall that is typically covered by the backsplash. If you already have a backsplash, you might have to consider how you plan to cover the new crack.
That should provide you with enough information to get the ball rolling on your project.
Shannon Pate