Yeah, on the starrett, mcmaster is very variable. There are times when the starrett price is very similar to any other place, and there are times when mcmaster carr's steel price is like 25% higher than the going rate at the discount parts places.
They are not, however, so competitive on brass that I've ever seen.
I've only bought steel when I've needed it, so I'm not quite as much of a price shopper, but I haven't had any from anywhere that didn't produce a good result.
I read yesterday or the day before that lie nielsen is dumping O1 steel because they've had quality problems with it. I don't know how air hardening steel is done in production, maybe it's done very quickly and that's the difference. Just about any way that you control the temperature reasonably with O1 provides good results. The biggest shame is that their bench chisels in O1 would've been far more desirable than the same thing in A2, and I know derek has opined before that vintage chisels don't hold an edge very well and thus extrapolated that onto oil hardening and water hardening steels, but that is a matter of hardness and not a matter of the alloy (the vintage chisels are certainly less hard by a slight amount).
Edge for edge, the O1 steel is ideal for chisel type stuff and small blades in the shop - and compared at the same hardness and same angle is easily equal to any of the other common steels right now in chisels, but it grinds easier and is more convenient to sharpen on any stone than A2, short of diamonds - especially if you count time to remove nicks. It's certainly adequate for planing, too, if someone is not trying to win a contest of the most 1/2 thousandth thick shavings from a plane blade.
So, anyway, O1 - i've never had any trouble with any type, sometimes mcmaster has about the same price and sometimes they don't, but I like the starrett stuff despite not having any issues really with any of it - even completely unknown stuff that someone has sold in lots on ebay that just says "O1" on it in black marker (presume those are just sellers cutting short pieces off of long stock).
The cost does, though, get appreciable if you start building things like panel planes out of the steel, but that is one place where I will pay for the starrett, too, because I know the stock will be dead flat, which is a big deal to someone who builds metal planes without machine tools.