It depends. The actual fiber is probably good for decades. But a lot of the active infrastructure requires upgrades in a 10 year or so cycle. FiOS started out in 2005 with BPON. Then they upgraded to GPON. Now they’re working on NGPON-2. This requires upgrading ONTs, (very expensive) OLTs, switches, not to mention adding capacity out from the COs to handle the additional traffic.
OLTs aren't that expensive, especially since you can potentially split the costs of each port over 128 subscribers. Obviously the total dollar costs add up when you put thousands of subscribers on one OLT, but the cost per subscriber is quite low.
NGPON-2 isn't being deployed at scale yet, so prices are still to come down, but GPON OLTs are bulk items. You can buy a GPON OLT for a few grand which ends up being a few bucks per subscriber.
Verizon upgraded to GPON in 2008, when prices were a lot higher. Back then, GPON line cards were in the $10-20k range. (And they're upgrading to NG-PON2 starting this year.) Also, their typical split is 1:16 or 1:32. So you're talking about $600+ per subscriber (maybe pushing a grand once you factor in cost new ONTs and cost of labor to install new ONTs). That's a couple of thousand dollars per subscriber over the amortization period (at least if you're hoping to keep up with the Joneses).
In 2006, Verizon's cost to pass a property was $850 and trending towards $700 in 2010. This includes not only the outside plant, but also the OLTs. The majority of the cost is in the outside plant, so the GPON OLTs are only a fraction of this.
Verizon deploys at scale and does not pay list prices. Furthermore Verizon would not be deploying NG-PON2 if it wasn't profitable and would definitely not be doing it if it was cutting into their margins. Therefore there is no reason to assume their NG-PON2 costs will be higher than their GPON costs.
