We tried our local Farmer's market and found it to be a very limited source of income. Farmers routinely showed up to dump products such as corn, eggs, watermelons in season that undercut the steady vendors. There was a lot of back biting and petty politics because there were few customers and more vendors to fight over them.
We then went an hour away to a more urban farmer's market that is steadily growing and are very happy with it. It's well worth the cost of the gas. The petty politics is much reduced because we are big enough to afford a full time market manager who is outstanding. There is enough money and upscale customers that allow for higher prices which reduces a lot of the back biting and infighting. The better pricing allows us to incorporate the cost of packaging into our prices.
You can get discount prices for packaging if you buy in bulk. On the internet many places give you FREE shipping for larger orders. The only packaging we buy is: egg cartons (buy every 3 to 4 year in bulk), plastic bags and pint containers. Most customers bring their own shopping bags and we keep used plastic bags for customers who don't bring them. You can get enough of the used ones just by saving your own grocery bags.
We did have a one time investment in an awning, tables, chairs and cloth (for table cloths) but I made my own and you can probably buy the plastic table cloths cheaper. We do routinely get business cards and periodically update a large sign.
There are many vendors at our Farmer's Market that make a very good living. It can be profitable, if you have children for free labor or focus on high dollar items. Yes, some people lie about how and where their products are produced but in the long run the ones who make the most money are those who are up front and honest with their customers.
Good luck and don't hesitate to change markets if you are not doing well.
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