Relic
You don't say what breed you paid £150 for a boar, which i think if its pedigree iis dirt cheap.
Bet you'd pay £400 for a pedigree puppy dog!! So why not more for an animal who's going to give you a litter woth a possible £400/litter!!!
And what do you mean by send him on his way? kill or sell on?
As Hilary's mum says introduce the girls one at a time or you'll get piglets all at once, this way you can stagger the farrowings, he always has company and your girls get one to one attention and will give you a better idea of when your litters due.
HTH
Mandy