Let me help to clear up a few things.....
-Lowering springs will lower your car a certain amount of inches and that's it. They have NO ride height adjustability. You may be able to have a certain lowering spring give different ride heights all depending on how stiff the struts/shocks are, but once they're installed on the car, the ride height will always be the same. You can install adjustable shocks/struts with lowering springs, but the adjustments usually only allow the "compression" to be set...in other words how much resistance the strut/shock has when being compressed.
-Sleeved struts (commonly known as coil overs) consist of a strut body with a threaded sleeve that allows the spring perch (the part that the bottom of the spring rests on) to be adjusted up or down by spinning it on the threaded sleeve. The lower spring perch is now adjustable along the the sleeve and thus the ride height can be adjusted. You must jack the car up off the ground to do any adjusting. The draw back to this type of coil over set up is that the spring is getting compressed (as well as the strut/shock) when ever the car is lowered below the stock setting. This isn't necessarily bad, but lowering the car will take away some of the travel of the strut/shock and also cause the spring to be compressed more than usual when the car is not under any load. (I hope I'm making sense...it's still early!) $800 for the Tein set up sounds like a good deal. They make great stuff.
-Real coil overs, like the FLT-A2 offer all the benefits of a sleeved coil over, but the ride height is independently adjustable from the spring preload. Imagine another adjustable "collar", below the adjustable spring perch collar, which allows the ride height adjustment without changing/compressing the springs and struts/shocks. You must remove the lower mount from the suspension to adjust the ride height. Now you can adjust the ride height without taking any travel away from the suspension.....and you can also adjust the spring height/preload so the car won't bottom out or bounce off the bump stops. This type of system is usually about $1500 or more and might be over kill for what most people want since it takes some time to set up properly. But once set up, it's suppose to be ultra nice.
For the $800 you can't go wrong with the Teins. Eibach makes great stuff too, but factor in about $200-$300 for springs, $500 for Bilsteins or Konis and you're already in coil over territory. Hope this helps more than confuses! Good luck!