2 heads of lettuce at $1 apiece is 2*$1=$<<2*1=2>>2.
4 tomatoes at $0.50 apiece is 4*$0.5=$<<4*0.5=2>>2.
Thus, each customer purchases $2+$2=$<<2+2=4>>4 in lettuce and tomatoes per month.
Therefore, if 500 customers per month spend $4 on lettuce and tomatoes, then the store will receive $4*500=$<<4*500=2000>>2000 per month on sales of lettuce and tomatoes.
#### 2000