The two tubes don't last forever. The value of yours would depend on the age of the tubes, and it might be difficult for you to estimate that. They are available for about $250 each, but probably not for years in the future. There are a couple of threads about that in APUG. In an email from the current manufacturer of the tubes they last "1,000 hours before you notice any difference" and presumably quite some time after that at reduced output.
New, the unit was priced $1400 retail, and $1300 approx at B&H.
It's a superb unit, and matched with an RH Designs StopClock Vario (to monitor the light output) it's a dream machine. I already have one, so I'm not in the market, sorry.