No food handlers permit required (at least for the Sandy Farmers market).
You do have to be a member of the Farm Bureau ($65/year) and the cost (in 2008) was $110 for a spot.
But, I've heard stories that folks that charge $5/dozen for farm fresh organic eggs at the Farmers market.
As for how many dozen we'd need? I dunno....
After all of my hens start laying, in August, I could probably come up with an extra 5-7 dozen a week.
That's not going to last too long at a farmers market.
But, if we had several people join together, we could probably sell everything.
Would be good advertisement for extras after the market closes too...