Lovely sign, but why undersell your lovely eggs? I think £1.50 for 6 is fine and still cheaper than supermarket free range eggs. (Just get her to paint a '1/2' in front of the 'dozen' on your sign.) However, maybe bantam eggs should be sold at a bit less than large hens eggs? I would think the idea is basically to help cover feed costs and you wouldn't do this at £1.50 per dozen.
How do you collect the money? My friend sells at the gate and he has a locked cash box superglued to a very solid large box, with his sign painted on the side of the box, and people just put the money in there without him having to keep coming to the door. He puts the boxes of eggs in a large coolbox, and people return the empty boxes to this so they don't blow away.
Next month's Practical Poultry magazine is going to have an article about the ins and outs of selling your own eggs, if anyone's interested.