Saying meth/water injection doesn't do anything but lose horsepower is just ignorant.
Depending on what you want to get out of a meth or meth/water injection setup, you can go a few different ways. Depending on which direction she decides to go with the car we may be running meth soon on Stephanie's SR. Unfortunatly some racing sanctions either don't allow you to run it or will count it as a power adder.
I've been running meth and or meth/water kits on customers cars for years. 700+ hp supra's on stock fuel with meth injection and pump gas. Running straight meth has plenty of bennifits. It can act like a fuel system and or race gas. You can run more timing and greatly reduce detonation when you run meth. I usually install these on customers cars when they have a daily driver but don't want to have massive injectors that will hit your pocket book hard everytime you lay into the car. They can run on the stock fuel, hence keeping stock gas mileage. The amount of meth sprayed for the power I usually run isn't much compared to running larger injectors when you compare the cost of meth versus premium these days. Sometimes you can find meth cheaper.
I would recomend having a stand alone if your going to run straight meth though. This way you can adjust everything you want and need when it actually sprays. I usually add some timing and have to pull some fuel when it is sprayed depending on the power the customer wants, you can do that with a piggyback or stock ecu.
If your looking at just using it for a partial anti-det device, then you can run it with stock ecu or whatever with good results.
http://www.snowperformance.net/
^ snowperformance has some of the best kits available on the market. This is probably the way to go if your not going to have a stand alone to run it. Their kits can run off of boost pressure switches so you can set it to spray when you need it to. Check out the website, I think it will offer most of the answers to your questions.
If your going to run a stand alone, you can always piece together your own kit for cheap as someone posted above. Pretty much everyone uses the shureflo pumps, and the rest of the hardware is just basic npt or -AN your choice.