The most cost-effective wallpaper paint in the United States is Behr Marquee. Behr Marquee is a high-quality, durable paint that offers excellent coverage and a wide range of colors. According to a survey by Consumer Reports, Behr Marquee is the most cost-effective paint brand, offering the best value for money compared to other leading brands. The average cost of Behr Marquee is around $30 to $40 per gallon, which is significantly lower than premium brands like Benjamin Moore or Sherwin-Williams that can cost up to $70 per gallon. Despite the lower price, Behr Marquee maintains high performance and durability, making it an ideal choice for those looking to save on wallpaper paint without compromising on quality.