You can buy nitro mix in quarts (about $10.00/qt + hazmat shipping cost) or gallons (about $25.00/gal +hazmat shipping cost).

You can run up to about 1-2% nitro without changing fuel delivery system significantly. Since nitro is almost 50% oxygen, you need to be careful with fuel metering to avoid a lean condition. Unfortunately, you also need a stabilizer to keep the nitro mixed uniformly with the gasoline (extra cost.)

It will stop detonation. With 1% nitro, you should be able to run 11-12:1 compression.

You'd need about two quarts of nitro in a 20 gallon tank to get to a little over 1%. So, $20.00 worth of nitro, $40.00 worth of gas and away you go. Is it worth it occasionally? Possibly. But if you build youself a 12:1 motor, you're going to have to run it all the time.