I honestly can't be bothered to read through 26 pages to see if anyone actually posted the correct maths here, so I will just do it:
Console - $500 Headset - $0 (you have it, so no cost) Adapter - $20 (guess) Live - $20 (using actual cost, for half a year to bring in line with the year's ps plus) Plug and play kit/rechargeable batteries - $20 (another guess, to bring in line with ds4 rechargeableness)
Total - $560
Console - $400 Headset - $100 (to give as good a headset for ps4 as you would have on XBO) Sale of included ps4 headset - ($20) (guess) Ps plus - $50 (assuming you can't get it cheaper, which sometimes you can, at least here in the uk) Rechargeableness of controller - $0 (it does)
Total - $530
Optional - PS Eye - $60 (depends on how much you would use kinect)
Total with kinect comparison - $590
It all comes down to how much you would use the kinect/eye. The batteries you cannot do without, and I presume you are a heavy online user hence the headset + online considerations, so those are pretty much essentials too, but if you are like many then the kinect is very much not an essential and can be ignored, in which case the ps4 is still cheaper.
If you were being super exact you should add some cost to the XBO headset, since if you were to buy a brand new ps4 headset it would last longer than your used XBO one, and the idea is to compare like for like as much as possible
Eg. If your XBO headset is 1 year old, and will last 3 more, and a new headset will last 4 years then $25 should be added to the XBO price.
I know the headset is a sunk cost, but the cost of replacement in the future is still relevant.
Source: I have a maths degree, and am a professional accountant.