What camera do you have? Alexa Classic? Are you looking into PL mount lenses for the ergonomics or simply because you have a PL mount camera? Lomos and Sigma Art look a world apart. What look are you after?
If your sensor is only S35 there are lots of good affordable options in Arri standard mount with a real vintage look if that's your thing. (Imo.) However most of these lenses were designed for Academy format and offer less coverage than their PL mount successors. I'm not sure if the Alexa Classic shoots 3.2k, but if it's just 2.8k then you have a ton of options in Arri standard mount, and these are inexpensive to convert to PL. The Lomos should be good, too.
Check out these adapters to start. The OCT18 and OCT19 ones are quite good.
http://rafcamera.com
I believe Leitax sells a mount conversion for the Alexa that's good and affordable, too. No experience with it.