Wow, I didn't know scouting had a demo badge!(Just kidding!) I assume this is for a civic service project? Depending on how many people are going to be involved, you might consider hand demolishing (using sledge hammers and crow bars to dismantle the building piece by piece; this is prbably your cheapest option). If you have an adult and the availabe funds you could rent a skidsteer loader with a grapple attachment and use it to mechanically demolish the building. Do you have to remove the slab and foundations? The skidsteer would help with that (rental w/attachment would be around $250/300 per day depending on your location). As far as methods, try to let gravity work for you, go from the top down, and always always always leave your self room to get out of the way!!