I wouldn't bother with selling videos through iStock. You'll only get a few dollars, sometimes less.

It varies.  Ignoring Connect sales, which get $0.01, I've had regular sales between $0.11 and $108.17, the latter presumably an extended license of some kind.  Don't expect many of those.

But then, I don't bother to upload videos there unless they've not sold elsewhere, as the return is so low - although strangely, I've occasionally found that some that don't sell elsewhere have been quite successful, at least in terms of downloads, on iStock.  But don't expect much in revenue.