It depends. Paint costs vary by brand, ease of application, adhesion, durability, and eco-friendliness.
However, across most paint brands and types, the average cost of a gallon of exterior paint is $31, ranging from $20 on the low end to $55 on the high end.
Below is a list of prices as of July 2013 of 1 gallon of exterior paint in a satin finish from each major U.S. brand:
Exterior Satin Paint:
Valspar – $33 Valspar Duramax Exterior Satin Paint and Primer in One
Glidden – $30 Glidden Premium High Gloss Interior and Exterior Paint
Olympic – $25 Olympic Exterior Satin Paint
Behr – $32 Behr Premium Plus Satin Enamel Exterior Paint
Clark + Kensington – $35 Clark + Kensington Paint and Primer in One Premium Exterior Satin Enamel
Sherwin Williams – $38 Sherwin Williams SuperPaint Exterior Acrylic Latex Paint
Benjamin Moore – $39 Benjamin Moore Regal Select Exterior Satin Paint