They need 1600 square feet / 400 square feet/gallon = <<1600/400=4>>4 gallons of paint for their walls.
Since they will do a second coating, then they would need 4 gallons x 2 = <<4*2=8>>8 gallons in all.
Eight gallons of paint will cost $45/gallon x 8 gallons = $<<45*8=360>>360.
Thus, Jason and Jeremy will each contribute $360/2 = $<<360/2=180>>180.
#### 180