6-94 lb bags of Portland. Which gets you 3000-ish psi. Of course it turns out better when it's done in a mixer, nearer 3500 psi, but not having a mixer has never been a deterrent to farmers or rural municipalities. I've seen plowed, disced, harrowed, n rototilled roads and slabs. All were fine for the purpose.
For a 6" slab it's a bag per 10 sqft.
And don't forget to wash off your machinery immediately after use. Concrete makes a mess of things if allowed to build up.
Just to clarify for the OP, that's 6x94 of portland cement powder. PLus tons of gravel and sand and a little lime.
Home brew ratio is usually 1/3 shovel of lime, 1 of cement, 3 of sand, 10 of gravel.
eta
1/3 shovel of lime, 1 of cement, 3 of sand for mortar
1 of cement, 3 of sand, 10 of gravel for concrete
If you have access and room, the most affordable option by far is mixing your own from scratch.
Bagged readimix is convenient if you can get a loaded pallet dropped close to the work. But costs about 4x the cost of a couple piles of raw ingredients.
It is a pain when the work is in the back yard in the suburbs thru small gates.
I go get 20 bags in my old 1/2 ton pickup and wheelbarrow it in back 3 bags at a time.
I can get 2x60 in that mixer and it goes quick.
Right now I'm just getting started on a large outdoor cooking setup with embedded propane and charcoal grills and a pizza oven, intending a cast in place concrete countertop but I'm running out of decent weather and I'm getting twitchy about attempting 12cu' / 30 bags in a monolithic pour in Vegas summertime. Don't think it will go well, too hot and dry here.