Why would seeds cost $5 each if the plant was legal to grow? The only reason they're so expensive is because of prohibition. Hemp seed would be sold in 50 pound sacks, like seed corn, and probably cost no more than $50.
I had to start with something $5 is what the local growers will pay if you find a seed in their Green Bud. See my disclaimer.
There are 43,560 square feet in an acre. If you gave each plant 16 square feet (a 4 foot square), you could put 2,722 plants on an acre of land.
Again lack of time to look up figures for an acre.
Why would you need any help tending to 800 plants or even 2,722? Most farm "labor" these days is done by implements a farmer hooks up to a tractor. As happens in countries that already grow pot as a field crop, you'd have to hire some people at harvest time, but that's it.
You are talking about specialized machinery. I am not sure these are available at this time. Although Hemp needs very little care. I don't know of any harvesting machinery or a machine to trim the buds and hang them to dry. There may be a packaging machine. It still needs someone to run it.
I posted to a make a point that the tax is not so high as Reggie supposed it to be.
Why didn't you provide us with a more accurate proposal based on your observations?