Years ago I bought an immaculate FD 50/1.2 L (red ring) - I thought I had paid “good money” for it then but a recent check of what their asking price was on eBay did bring a wry smile to my face.
However there were several f1.2 50’s made by Canon. From the FL through to cheaper and more expensive versions in FD mount. As far as I am concerned the very sharp FL 50/1.4 is cheaper, sharper, smaller and a better buy in my opinion than the FL 50/1.2.
I can't imagine the f/1.4 is sharper, unless you mean @ f/1.4 vs. f/1.2. Of course, slower lenses are always cheaper... but I disagree about which is the better buy.
The FL 58mm f/1.2 was essentially the premium normal lens introduced to go with the
Canon Pellix. It was always lower priced than it should have been, and sold in unusually high quantities, because it essentially made up for the light loss from the fixed semi-transparent pellicle mirror in the Pellix. Although this might sound like Sony's SLT, Sony uses an EVF in their SLT bodies, with the SLT mirror just diverting some light to the PDAF sensor; the Pellix OVF was pretty dark because it only got 1/3 of the lens light. The FL 55mm f/1.2 is optically improved over the FL 58mm f/1.2, but pricing stayed very aggressive.
In any case, I paid about $200 for my FL 55mm f/1.2, but I've seen more than one clean copy under $100! I actually saw one go for $50!!!! Even $200 is an incredible buy, because this really was "L"-quality glass in its day -- and it really does deliver a better than average rendering for an f/1.2. I'd say the lens is optically worth more like $300. I do like my Minolta Rokkor 58mm f/1.2 better, but I don't think it delivers IQ worth more than about $350, and they often sell for MUCH more than that. Pricing on MOST f/1.2 lenses is much higher than is really justified by IQ, but I think the FL 55mm f/1.2 is the exception.