I thought I had replied a while ago on this, but it must have been my imagination. Around here as a rule of thumb, I start with $1/lb for the cost of new rolled steel - as long as I'm buying it in the same size piece they get it delivered in. Fabricated items like tube will be higher. If they have to cut it, they would likely charge extra too.
Before winter I bought a 20' C5x6.7 & L1-1/4x3/16 to do a trailer modification, and the price for that was almost $1/lb down to the penny. This place is new and is a fab shop, not a sales shop, so they order on demand, and it would be delivered to them next day/2 day max. if i need something same day, there is another fab place that has a reasonable amount of lighter materials in stock, up to 4" ballpark. their prices tend to be higher - $1.25/lb or more last time I did the math, and they keep cut-offs to sell at the same price - just no cutting charge when you buy a cut-off.
Not recently, but at times in the past i've found some recycling places that have had clean cut-offs for $0.35~0.50/lb, but most recycling places aren't selling to the public here. Have not seen clean usable steel at "scrap" prices in decades. I did find some chunky cut-offs at Marden's a year ago - 3"+ thick rounds and plates in 10-20lb chunks. i bought a few to have on the racks for future tool and fixture build projects.
It's a far cry from when i was young and just starting out back in the 90's and i could buy through my employer at cost - i remember paying as low as $0.17/lb for new angle bar, and $0.25 for most items, $0.35 for tube.
As a reference for people - steel weighs 490lb per cubic foot. just do the math to break that down. 1/2" plate ends up at 20.4lb/sf, so a 4x8 sheet would be 653lb. assuming that is a stock size from the supplier, which it would likely be, making $600 about right, more or less.