I wouldn't use the wheat the farmers plant. It might be treated with something that might linger in the young shoots.

I can buy organic whole wheat berries at my supermarket (Wegman's in Eastern PA) for about a dollar a pound.

I can't help you with what kind of juicer you'd need.

As far as how to do it, there seem to be pretty good instructions on the SproutPeople website. I have no connection to SproutPeople and I'm not promoting them. But their pages have LOTS of useful information for how to do it. I've sprouted wheat before (just in a small jar), but I've never grown it into wheatgrass.

Their page on sprouting grass:
http://www.sproutpeople.com/seed/grass.html

Their page on their wheatgrass kit (you don't need to buy the kit, of course, but you can use the information to improvise at home):
http://www.sproutpeople.com/seed/kit/wgkit.html#Anchor-6296

(I've never posted links here, so I hope this works well enough.)

Hey there - honestly, it's not that expensive to grow. I have a blog that has a spreadsheet attached to the page that breaks down the cost see http://wickedwheatgrass.com/how-to-grow-wheatgras/the-cost-of-growing-wheatgrass/ . I managed to get the cost of a shot to $0.20 (letting the wheatgrass grow a second time) I'm not selling anything on there and give a straight account to growing and managing wheatgrass. It is great for you so I highly recommend growing it :) - Happy Juicing!

Here is a link that might be useful: Cost of growing wheatgrass