Pete,
Presume this is a few to family and friends
People have little idea what a 1/4 or 1/2 pig is in terms of size (and cost), and if you sell the parts, then most will opt for pork leg and chops, leaving shoulders and belly which whilst delicious will quickly fill your freezer, and yes you have to start charging differential prices.
One good way to sell is "Pork selection Boxes" which will contain chops, sausages and joints
You can then price these - so say they have the option of a £30 box, a £45 box or a £60 box - of course they can but more than one box if they want more!
You can then decide how much per kg to charge. I normally start with a quick troll round Tesco to get an idea of what a supermarket price is, and then decide how much more than this I want to price at. This will depend on how desperate you are to get the first sales (once people have tried price tends to become unimportant - they normally snap your hands off for the second lot). A reasonable premium should be charged, taking into account your costs, and you can find anything from a few % above to twice or three times - look at river cottage prices if you want to shock yourself!
Once you collect, you can then sort into the boxes, small joints for aunt sally who is just her and hubby and more chops and sausages, and Billy's large family can have that large leg joint. Fred family live on sausages, so a few more for them.
Don't forget to have a box for yourself !