If you look after your hybrids well as in housing, heat, ventilation, light, disease then hybrids will lay 2 eggs a day, we charge extra for our double yolks as well.
Your hybrid price at £6 seems a little high, also your bedding visit a commercial unit that may well educate you a little. Our bedding costs are 0 though we do collect a small amount of hay.
3p a box is good but to be fair we ask for boxes back I guess we use 1 in 6 new = less than 1p each
Your food bill seems low for layers, if your on pellets you may consider going to mash
If you let them out they will never do 2 a day in fact you probably wont do 300 a year maybe more hens and less feed costs ?
We have 95 ish though only get about 72 eggs a day this is because I now work and cannot devote the time/effort involved in lighting/heating etc, so they have adlib feeders, then out to play from 11 ish each day
we feed layers mash and sprouted wheat our feed bill is approx. 2-3p a day per bird
Either way buy the birds make a little extra and see how it goes
Declare every penny to the tax man saves having to look over your shoulder, plus all the tax helps keep our country so good.