Having just put a small cornfield on my own layout, I can tell you all that those plants are not cheap. With just under 400 plants on my own 'farm' setting (and a grouping of them bought used off eBay), I describe it as my "$100 cornfield" as that's about how much the plants alone cost.
Never mind the time and effort you have to do to put out the rows, drill the holes, then make sure you get them 'planted' together to look right!
