Well I think this is different for everyone. I personally had the rationale that my REP was close enough to the original that the only thing which stood out was the band itself. So I went ahead and bought two GEN straps from an official Panerai dealer. The cost was pretty high, the average is about 180USD before taxes, but I would say it was a worthwhile investment for me as they really added the perception of a genuine watch.
Now since this time, I have ordered a new set of straps from a strap dealer named Greg Stevens Designs (GSD), a few pictures of the new strap I've order are below. The cost on these are around 165 with shipping and include the buckle. I've not received these yet but I am looking forward to putting them on. If you're interested in GSD you can visit photobucket.com and enter gregstraps/gregstraps for UID and PWD and see the entire collection.
HTH,
Eddie