murdock - both ways are quite ok, bearing in mind that you have to run power to the cameras as well. You could have 2 x 4 channel dvr's if you wanted to keep the buildings seperate. You could cuse RG59 cable with the twin core power cable joined to it - then you would not need the baluns. Both work just as well - personally we use RG59 for shorter distances and normally cat 5 cable with baluns when the cameras are going to be further away from the dvr.

Cost effective - you would have to check exactly what you would need to minimize the left over cable - but probably RG59 with bnc's would be cheaper. If it is for home "movement" cameras is not really neccessary as long as you can cover the entire area with all the camera's.

I would just use one power supply from the one dvr - make sure it is a big enough power supply for the 8 camera's. This would eliminate having to run more cables to the cameras from the other building - keep it neat and clean - everything runs from the dvr and power supply to all the cameras.