If you are looking for cost efficiency then you probably should be looking at T5HO's. There are a lot of different choices out there and it really depends on your plans for what type of corals will go in the tank.
Some examples of a cheap option would be the Odyssea one here
http://www.aquatraders.com/24-96W-ho...e-advance.aspx
Or you could go with the Sunblaze fixtures near the bottom of this page:
http://www.prairiereefsupplies.ca/index.php?id=95
Another option might be moving up the scale a little with this:
http://www.jlaquatics.com/product/sl...C+4+x+24W.html
It really depends on what you hope to achieve.
As for your other questions...If your frag system is completely separated from everything, I think you could get by with some good powerheads and regular water changes.
It's important to note that I don't have my own frag system so you might want to wait for more input from other here who have one.