Happy Hippy, £100 is maybe slightly on the optimistic side, but not by much, and when doing a few in a batch, probably is about right.
Cost of Weaner - £35 for traditional breeds (i.e OSB, British Lop etc) or £1.60 per kilo for commercial cross breeds (making a 15 kilo weaner £24).
Cost of feeding up until 24 weeks - £36, based upon 315 lb / 144 Kilo, at £0.25 a kilo (or £250 a ton).
Straw - £20 based upon 8 bales at £2.50 a bale (based upon two pigs having one bale a week).
Slaughter and Butchery - £35.
So just going on what you included, that would equate to £106, including the straw it would be £126.
However, that cost would reduce if I was buying the cross bred weaners, and if running a larger batch the straw etc cost per pig would reduce.
My biggest savings and feed and butchery.
But I can't get anywhere near what some people on here charge for my meat. I sold two half pigs the other day, butchered and packaged nicely, weighing about 33 kilo per half pig, for £90.