>>268497708
Just correcting a few things, the index is expensive as a full set but they do work with gen 1 base stations, so you can get just the hmd and link box for 500, though if the issue is the base station you might just need to shell out for the full 1000 kit. 
Cv1 offers some comforts over the Rift S, being a 90hz screen and adjustable ipd slider on the headset, otherwise the rift s offers the best inside out tracking for more of a plug and play experience and a higher resolution screen at 80hz. 
As for the last 2 you're pretty much right, the cosmos seems doa and the pro is a side grade to the vive and costs almost as much as an index for the hmd only, costing 800 dollars after a year on the market.