goodiepocketI understand the point you are trying to make and when on a budget, yes...those options would work. However, for each of those lenses you basically talked me/anyone out of wanting to buy one. Why buy a cheap lens, struggle with such issues and probably end up having to buy another cheap lens to replace it down the road...when (if you have the funds) you could buy a good lens and have it last for a MUCH longer time. IMO, saving and spending the extra money is completely worth it.
I say this with a full lineup of vintage Nikkor glass (24,35,50,35-70,80-200) as well. I have gotten some beautiful results with these lenses and they are a light and cheap solution. Getting vintage lenses takes some time and research to make sure you are getting the correct year/model of each lens and they still have their visual drawbacks (other than some of the $$$ vintage lenses).
Obviously the example of an Otus is overkill for most photographers/videographers, but it is one that I could provide as a personal experience. My point is, I don't think though that you should believe that unless you are doing 'studio work' that you should have the best lenses you can afford. Glass is a great investment and there's a lot more that goes into such lenses than just the optics that makes it worth the increase in price...
I mean, the drawbacks of the 50 f1.8 mk2 are obvious... But for 70 bucks or something used, honestly it's a throw-away kinda thing. If any of the others had a problem, or you were traveling and wanted to lighten the load, it's a great option. That's why would have always had one even if I had nicer glass in that focal length had I stayed with Canon. Hell, if I get a Nikkor 50 f1.4 I'm still keeping around my 50 1.8D for virtually the exact same reasons (plus, then one can just sit on my film camera semi-permanantly).
You can even get the 50 f1.8 mk1 if you want to avoid the more startling quality issues for 150$... gives you a better focus ring, a focus window so you can figure out your infinity stop, and a metal mount with the same high quality glass.
As for vintage glass... you can find an M42 mount 50mm for like 10-20 bucks and adapt it for another 5-10. For the longest time I was using old pentax glass on my Canon for this very reason. Old 50's are a dime a dozen, they're all mostly high quality, and very affordable. For video they're absolutely worth having in any situation.
Both the Sigma and the Canon 50 1.4's are good lenses. I like them both optically (especially the sigma) but I had to point out the issues I've seen with both. Are they worth 3 or so times as much to have a 7 or 8 blade diaphragm and manual focus override? That's your decision.. I was just posting my gripes about each rather than sugarcoating it and telling you exactly which one you should buy.