Setting aside the DIY and hacking spirit of the project, let's remember that, with the commonly accepted figure of 2,500 kcal/day for an adult male, a whole iceberg lettuce (~600g) provides about ~87 kcal which is roughly 3.5% of what one's need.

So what though? I can get all the calories I need from $0.50 of rice but I still need crunchy things and protein.