I told this to someone already today , and decided to make a post.
The 50 dollar robot can be easily modified for line following. Just bend the photoresistors to face the ground on a 90 degree angle. Make them 2 inches apart. Then add an LED on the front. Play around with the values of the photoresistors in the code and thats it.
Hopefully, someone who has built the 50 dollar robot can demonstrate this on their robot and perhaps document it a bit.