Realistically you only need to change the 2 rear tyres (assuming the puncture cannot be fixed - which it does sound like). Alternately, there are often some good deals around on buying all 4 tyres, look at ATS or similar (but as well as looking online do give them a call, as sometimes they have better deals onsite than they have on the web (on my previous Evo, I got 30% discount rather than 25% advertised on the web).
Often there is little or no discount for 2 tyres, but you can usually get 4 tyres for the price of 3. Michelin I think have a deal on at the moment, which might be worth a look at (and check price against Costco if you are a member).
I just fitted 2 Michelin PS3's to the front of mine due to a puncture, and was advised if having one that the difference in tread between new and the "used" Conti on there would possibly cause issues. So 2 PS3's it was (and very happy with them too)