I highly suggest bluestone (what one called blue metal, but it is not metal, it is slate). Thois stuff will not track in to the house on shoes, is environmental friendly, and is cheaper than anything in the long run and a "one shot". Oils and stuff are hard on homes when you track it in. Concrete work on your own with "borrowed or seconds and 1/2 loads concoete is a PITA, been there, done that, learned the lessons.
I had a 40 x 25 garage with a sand base floor. Dusty as heck. Wanted to concrete it, even tried spreading concrete and hoping it would do something...it did, got more dusty, and the parts that solidified just created big soft rocks, tried a bit of oil spray, just created clods and problems.
I finally got enough bluestone an agregate we have up in New England, also slate (ledge) chippings elsewhere, and put it in about 1.0 to 1.5 inch thick, held back about 1/4 ton for a while in a pile. Cost $75.00 for two tons, you will surely pay less, but this was the minimum price for a three ton load, I only ordered two.....
Dusty at first and kind of rough, but the slate as you walk and drive on it gets very flat and the dust solidifies into quite a hard pack, kind of as mentioned above. Does not hold moisture, lets it off fast as well. gets smooth or even smoother than pavement, almost as hard. Only took two weeks!!!!
The 1/4 ton I held back I filled in the car ruts with after a month and 1/2. They never returned. This was better than any concrete job, paving job, and held up well. 1/2 to 3/4 inch works well in most cases in normal shed use.
I also did this on a seasonal campsite, replaced sand and whitestone, which was both dusty and hard on the feet and shoes, and tracked into my camper easy (1/4 acre campsite, 75 foot yard of dirt and mud). Changed it all, the local bluestone provider went crazy with sales there. Only .5 inch cover there and it filled in the low spots and leveled very nice!
I moved five years later, the floor in that garage was such that I could hold jacks for cars, could roll around on it working on cars and get only sligtly dirty, and my lathe did not have dust problems.
In New England, this is pavement for private roads and driveways, and it looks really great! Lasts forever, better than gravel fill.
In my new home l (20 x 20) porch in my yard recently, used about 1/2 ton bluestone for 1.5 inch thick, lasted the wonter...the snow blower did not raise it up and I can walk barefooted on it two years later. the snow shovel would raise it with effort, but it stays in place, great stuff.