Hi and welcome to the forum!
Weaners:
The price varies throughout the country, here in Herts it's at least £50 per weaner.
Housing:
You have a barn - is it secure enough? If little weaners use if for sleeping, they'll also try and get out of the tiniest gap to explore the world around them before you've even arrived to give them breakfast. If the weaners live outside, you can make a very sturdy shelter cheaply using pallets and a waterproof covering for the roof. Plenty of examples on this forum and rest of the internet.
Fencing:
Electric is best is very quick to install and move, it gives them a mild but annoying shock. You need to stay with them the first day, though, as they might jump forwards through the wires instead of backwards
Fixed fencing takes ages to install and you can't move the pens around easily.
Once you've bought it, you can use it for years. Our energiser was about £75. 60 stakes and 600m of wire were about £100 in total. We also had to buy an extra car battery to use with the energiser as we didn't have a spare one left.
Field:
Pigs need space to run around in and soil to root in (their strong, natural instinct), but beware: they're little rotovators! After a few months of piggy-on-the-field, the field is pretty much plant-free.

You don't need to pay for field rental, so that saves you quite a bit. Remember, they need plenty of shade!
Water:
You'll need a low bucket in a car tyre for water (the tyre helps a great deal in stopping the little piggies of turning it over and then spending a day in hot weather without water), and a dry bit of ground to put their feed on or a big enough trough. Last year, we used 2 huge round wooden plates which were free, but were further from a tap and had to buy an aquaroll from ebay which was, I think, £30.
Feed:
Feedwise, we give them mostly grain and beans from a nearby farm but most people feed them pelleted food. Again, lots of topics on the feed on this forum and some of the individual breed society's websites. Price varies between brands and delivery company, bulk or bagged, organic or not etc. These days I think non-organic is about £7 for a 20-kilo bag, again in Herts. Theoretically, they eat (in pelleted food) a pound per day per month that they are old, up to a maximum of 6 lbs. So a 4-month old would eat 4lbs per day. Some people don't feed the 5 and 6 month old weaners the full amount, though, they cap it at 4lbs.
Transport:
You can pick weaners up by car, but will need a proper livestock trailer for slaughter. You may be able to borrow one from a neighbouring farmer as we do - no livestock hire available here at all, only horse trailers.
Slaughter and butchering:
Again, prices vary. We pay for slaughter per the weight of the pig, around £40 per entire 6-month old GOS boar. Butchery per whole pig is around £35-£40.
And then there's straw (a few bales per summer), the odd vet bill, the new memory card for the camera

What you get in return from 2 pigs is a whole years's worth of the best tasting pork!
Do indeed take a day course or visit other pig keepers - it's very interesting to see how others organise things!
