The 85 million is quite reasonable if you consider that it includes the cost of spares, which for the engines and radar could add up to be a lot. Export deals can't be 1-1-ed to domestic production because domestic production is for the runway price, whereas export deals usually include a support package.
On one of the posts deleted, I think a remark that needs to be kept is that the Su-35 has a longer range and payload than J-11Bs. The J-11B is on the Su-27 baseline, which means it only has about 4000 kg in payload capacity. The Su-30s remedy this, of course, but they trade off about 15% range. The Su-35 uses composites to increase fuel capacity from 9500 to 11500, giving you slightly more range than the Su-27 (less than 2%) while giving you a robust payload level. I think in PLA service, the Su-35s will be used primarily for strike missions, perhaps using Russian armament as well, which is a field where China is slightly behind.
Regarding the avionics, in an ideal case the avionics would be Chinese, but if you had Chinese avionics, you'd need to recertify and rework all the Russian munitions for the Chinese fire control system. It's not undoable, of course, but at least with initial versions you will want Irbis-E for plug-and-play use of Russian AAM and AshM. A J-11D-class AESA is better, of course, but it's only a 25% range trade-off and against ground targets where the Su-35 has the most advantage over existing planes in the PLAAF (J-10B is better WVR, J-11D better BVR) you're more likely going to be limited by missile range instead of radar range.