One way to make a box of eggs more appealling or valuable if you have local cheap competition is to use breeds that lay different coloured eggs - blue from Legbars or araucanas, dark brown from Marans, welsummers or barnevelders, white from leghorns, etc.
That way, if you have room, inclination and cockerels, you can also sell hatching eggs when it suits you. Depending on breed and locality, these can go for £1 - £2 per egg (or less, or more!)