When you do work out your price, as mentioned above, do remember postage and packaging.
I try, where possible, to have the photos delivered direct to the customer and the invoice to me. This generally works out cheaper. Of course if you are printing your own then the cost will go up as you get the hardbacked envelops, plastic wraps etc.
If you are not to sure about the quality of your prints or the colour correction usually offered then its best to get a print sent to you first. Some companies will even do this for free.
Price wise I would say your a little on the low side and could probably get more ie:
£5 for 6x4
£9-10 for 9x6
£15ish for 12x8
I seem to get regular re-prints from weddings at these prices and have seen other togs sell for much more.
Have fun