I took weaners to market once (Large Blacks in an October sale) the bidding only went to £5 each, I brought them home and vowed never again! The demand for pigs at our local mart just isn't there.
I sell privately, usually via word of mouth, our website, TAS, breed societies and Facebook. Don't keep the traditional breeds anymore, but when we did I sold weaners at approx £65 - the cost of raising them (without BPA fees added) worked out at £53 per piglet based on an average litter size of 8.......thankfully the people who bought from us could see they were getting good stock and thought them worth it but it still wasn't viable for us to continue keeping the big breeds. We keep kunekune, meat weaners sell for around £90 each and registered pigs at £125 - these prices include registration (where applicable), worming, vaccinations, membership to the BKKPS for a year and a 25kg bag of feed, plus aftercare and advice/support for the life of the pigs (and often beyond).
Some go as outdoor pets, a lot go as pedigree breeding stock and the rest are destined for pork - we raise some ourselves but demand for weaners for the freezer is rising. Selling finished product to the public needs a bit more work/planning but generally gives a better return than a finished carcass to a butcher (that's assuming you are lucky enough to find a butcher who wants them - they usually need a plentiful supply and the occasional pig of unknown quality isn't likely to appeal I'm afraid)
HTH