I don't know the answers exactly but I guess you need to know the costs and how much per year/month you can afford to spend on the tubes.
I see the RECI ones state 10,000 hours. I have read they get stale sitting around but that people have pulled out ones not used for a couple years and it was fine.
I think it would be fair to say that you would not pay more than $300/year for an 80W RECI and everyone that has one would say thats on the high side.