Hi Vicky
Sound OTT to me, but it depends on a number of factors.
1. The heat-transfer method of printing is cheaper than screen printing, but the colours are not so robust. Heat-transfer should cost £9-10 for just a few shirts, and it is not dependant on the picture or number of colours.
2. Screen printing does depend on the number of colours - each individual colour, front and back, requires a separate screen image, and a separate print pass, and it is the screen set-up that costs, so can't say what price would be reasonable without knowing this, but it makes the shirts expensive if there are only a few to be printed.
Would have been able to help out more, but I'm off on hols in an hour.
Best of luck
Del