From what I've heard the J-31 cost around 60% as much as the J-20. I think that China and most of the countries not named U.S.A. will primarily be fielding 4th or 4++ gen fighters in the near future.
South Korea, Japan, and Australia will all be getting the F-35! possibly India??? but who knows, India is still "dreaming" of FGFA???, but China will no doubt move ahead on J-20 production, even though there is little doubt that the Carriers have priority at this particular juncture. Other Air Force Brats on here agree with the "big Brat", I believe the Navy in the PLA has the clout at present, and the idea of an aircraft carrier, and the "sand bar bases", which in effect will function as Satelite Carriers at anchor, will function as a "forward operating area", to project power into and through the SCS.
While J-20s could conceivably be based on these sandbars, they likely will not. More likely to be populated by the erasable Flanker, in significant numbers, with full fuel and weapons, 10,000 will be a "NO SWEAT", ops area. The J-20s will be used in pairs, and likely "rotate" through just as the US uses our relatively more scarce F-22s, but we shall see?? The Marines will have 6 F-35Bs cruising the Far East very soon, and the J-20's will likely fly out to meet them on their initial "operational combat air patrols"! write it down, you heard it here first!