Notice he said wheat. This means he'll be turning it into wheat flour.
I get around 150 LP for my wheat flour (each one).
Therefore with a 5x5 wheat field (25 wheat).
You'd obtain 25 x36 LP for harvesting.
You'd obtain 25 x36 LP for replanting.
You'd obtain 25 xWF LP for wheat flour grinding.
Sticking my numbers in (150 LP each ; q80 ish wheat)
900 +900 + 3750 = 5,550
For a small 5x5 wheat field :\/ Of only q80
That would take under 30minutes to handle with a proper setup.
(You could make it into bread dough if you have a well for even more coolness)
I'm not sure how much Pea Pie or other doughs give on top of that, but it's enough to keep you satisfied for sure.