£1.20 is the bottom price in my opinion far far too low. 10 years ago people were selling around this price. I think £1.50 is more the norm. I am more semi commercial £2 for 6. I have done various costings allowing for the odd med, boxes, buying etc and it costs are higher than you think.
Sadly if farmers are selling this cheap then they havent sat down to work out overheads (as a farmer I spend a lot of time doing this) Labour, boxes, labels, odd vet, meds, purchase, dispatching, fuel, food, supplements, bedding all add up to around 90p for a box. Think I worked mine out at £1.20 overheads per box. Look at the supermarket prices for real free range its around £2 - £2.50.
Dont be ashamed to make a profit if you asked a friend to pop over to decorate yr living home its hardly likely they wont factor in a profit so why should you sell eggs so cheap.