If you've read and read, then you already know that there are no guarantees. For DIY, electrolysis with a probe is the only permanent option, either a One-Touch or Pro unit, or something you put together yourself ( http://www.geocities.com/hairfreethere/
All permanent methods have some risk of damaging your skin, especially if you are learning on yourself with little guidance.
Cost efficiency depends on how much your time is worth, how much work you need done, the availability of pros in your area instead of DIY, and how proficient you can become at DIY. The One-Touch is only $30 and can work for a small area, but because it is slow it may not be cost efficient for major areas.
I went for it and I am happy I did. No more shaving and plucking, just zap and gone forever.