www.elitefts.com has pictures, and sells them. I'd start with mini-bands personally, which is what I have.

Chains are going to cost a lot more to ship

Band tension increases as tension increases (distance traveled), chain weight increases as they get picked up off the floor.

Thanks bro.

How would I attach it to the benchbar? Do I need a powerrack or can I just use a regular benchpress?

depending on how the bench is made you can attach the band to the uprights or supports and in a pinch you can use a large dumbell to loop the band around .
also get some measurements for the chains and buy the at the local lowes/home depot/hardware/etc. instead of paying shipping .

If the powerrack I use looks something like this:


Where would I put the other half of the band?

unless the bands will fit under the crosspiece you will probablly need the dumbells