That's very difficult to answer without seeing the house. As one poster said, the prep is the most important part. On newer homes that don't have a lot of peeling paint, the prep can be very minimal even as low as a couple or a few hundred dollars for the prep labor.
On a 100 year old home with 12 coats of peeling paint on it, then the prep costs can be very high and can easily exceed 50% of the job's labor cost.
A 2100 sq ft two story home could easily cost $1000 just for the labor to prep for the paint job. That number could climb too. Throw in lots of caullking or window glazing, and you could be talking a couple or a few hundred dollars more for labor.
Painting that home with one coat of paint and a different color on the trim could run roughly $1000 or more just for labor. Add a second coat and that could cost close to another $1000 for labor.
For paint, you may need 20 gallons of paint. You can pay from $30-$70 for a gallon of good quality exterior paint. The manufacturer of the paint should be specified in any painting contract. Otherwise, the contractor could bid at a Sherwin-Williams $60 per gallon paint and then paint the house with $35 Valspar and pocket the difference. $25 dollars per gallon times 20 gallons? That's a pretty penny too.