You can get nice CBT arrays for less than $2 grand a tower. I can tell you right now with a single round tweeter, and a couple 6.5's you are not going to have great dispersion in the upper end, and you will have next to nothing for low end extension, and you will have common beaming issues seeing as you are using a flat array.
If you want to look at some great array designs....have a look here - Speaker Design Works
If you were really serious, you would do a cbt style array, that can be used as a l/c/r and surrounds.
Have a visit to the AVSforum, and look around. You can get into Genelec's for the price you are proposing.
Well if you want only on axis sound, look at some good point source drivers and use the concave array. You can localize very well. Toss in an 8 or 10" in the base to give you some lfe using the floor as a loading wall.
Horns are good, just limited range of frequency, unless you want to get real crazy with a multi horn setup in the same enclosure. Not really directional though unless the mouth is really thought out.
And yes I have been researching the home speaker thing for a long time now. Planning the HT room right now actually, so when I can do the concrete work, it will be go time.