Dave,
You have made the classic mistake , made by people who come from salaried employment into running their own CC business .
To run a successful business you need to invest and repair and replace equipment.
Your £20,000 set up will be worth , say £5,000 in five years time, thats depeciation of £3,000 a year ,£60 a week!
Repairs approx £1000 a year,insurances £1,000 a year,etc
Point being that when you were salaried all expenses in relation to your job were taken off before you were paid , now its the other way round.It probably cost Pirelli £60,000 a year to employ you.
I am a great believer that the maths when done properly never lie , so don't underprice yourself , your worth more than that.If you want to offer a low price on a particular job because you need the money thats fine but don't fall into the trap of being too cheap.
cheers
Doug