Too many speeds
Some people (actually, one person on the Cycling UK Forum) report excellent longevity from Campagnolo 10-speed chain. This person, however, achieves that by cleaning their chain more often and thoroughly than most people would want to even if they had the time! So I think the general observation that 10-speed equipment wears out faster and costs more to keep on the road (than is sensible for everyday transport) holds true. So I sympathise with your wish to simplify to 7-speed. But I wouldn’t go that far: 8-speed uses the same type of chain and will be easier to source quality parts for.
Unless you have suitable old 7- or 8-speed mechs and shifters, in good condition, this won’t be a cheap exercise and will take a long time to pay for itself in less pricy chains. And unless you have old Campagnolo mechs and shifters, you had better switch to Shimano, because Campag haven’t made anything 8-speed for ages. But here’s a thing: your Campag 10-speed right-hand shifter and a Shimano 8-speed shifter both pull exactly the same amount of cable with each click. Swap the Campag rear mech for any decent 8 or 9-speed Shimano mech and fit a Shimano 8-speed cassette and you’re all set. It should also be possible to fit a replacement Shimano HG-compatible freewheel body into a Khamsin freehub (provided it’s pre-2014), but this part is (a) hard to find and (b) likely to cost more than two 10-speed chains.
Alternatively, you could switch to 9-speed and stick with Campagnolo. Campagnolo have pulled the plug on 9-speed too, but you can still get 9-speed Campag cassettes, which will fit your hub just as well as 10-speed. Your existing rear mech and shifters will probably do, once the indexing cam in the right-hand shifter has been replaced with the different part for 9-speed. This is a tricky operation, best performed by a Campag specialist such as Mercian Cycles in Derby. A simplification to 9-speed still provides access to cheaper chains.
This was first published in the April / May 2015 edition of Cycling UK's Cycle magazine.