I paid about $6 per fixture....but note that they do not have trims yet....that could run $10 or more per fixture depending on what I decide on.
Also note that there could be an issue with building codes....depending on your area, you might be required to use pin style recesed fixtures (built in ballest)....reason...so that it's impossible to use incandescent bulbs.....
Right now I'm using 120 equiv bulbs...about 20W actual power....
There are a lot of variables regarding light output...who makes the light, the color freq...etc....but for the most part you can assume that 3-4 cans like I have using 20w CFL's is = to one 4' 2-bulb fixture....so you can assume you would need about 6-8 cans to = one 8' 2-bulb fixture....
One of the reasons I'm using cans is that I don't have the room to fit a recessed 4' fixture.....I do a lot of wood working....hence, I don't want anything hanging down....