if you go and find a HD DVD drive somewhere (they are really cheap since no one uses them) you can remove the high powered laser from it and make your own laser via instructions on internet

That is probally the cheapest way to get a laser that can pop ballons from a great distance.

the most powerful lasers are the infared lasers, but you gotta be careful because you cant see the beam without night vision and you could unintentionally destroy someones eyes