Agree with what the others have said re. cross breeds v pedigree. What's the point in buying cheap when you can buy pedigree, put to a pedigree boar, and then potentially double your market (meat weaners and pedigree breeding stock)? You'll also be helping keep the breed going.
And, as pointed out earlier, you shouldn't be thinking of keeping one lone gilt when the other two go.
Lots of people make the mistake of hanging onto one gilt for breeding just because they can.
Surely these aren't the only weaners available in your area. Where are you? Shop around and get the best you can afford if you want breeding stock. By all means buy cheap meat weaners to raise for pork, but be more selective with anything you intend keeping. You'll be glad in the long run.