Peter,
I've thought before about setting up a farm stand. My intuition (I haven't tested this) is that people will respond well to a sign that says, "SAME PRICE AS MEIJER ORGANIC AND WAY BETTER. GROWN RIGHT OVER THERE ->"
In Michigan, Meijer is the grocery store that's for people who don't like Walmart, but don't want to think about it hard
enough to find a CSA or farmer's market. It's the good store, somehow. Mostly because it's not Walmart. I guess.
In any case, everybody knows Meijer and more or less trusts them. Meijer doesn't get picketed.
If you want to write a short list of what you think you might grow, I'll go the Jackson Meijer and check prices for you. You can count on those to be minimum retail prices. Absolutely everybody will be willing to give you at least as much for your produce as Meijer organic, if you're telling them anything about the quality of your goods.
And that
should represent a decent real-world, achievable price to make plans around. (And then maybe you can do better even than that.
)