For those prices, I'd get four of them at least and let them pair up on their own. The aggression towards each other might be intense in a tank of that size till you get a pair, so more pikes to split it up would be better.
Then once you DO get a pair, and you'll know when you do, you would be wise to remove the other two. A single pair would be about all you would want to do in that tank. Or you could just have a solo pike in there, but they look so much better as a pair!