O1 Tool Steel!
Can be bought in very knifemaker friendly sizes (4x40x500, 3x30x500, 3x50x500 etc)
It is sold as gauge plate (fully annealed and precision ground) from a few different companies. I mostly dealt with Special Steels in Auckland. Email them for a price list of all their sizes. I was buying 4x40x500 for around $23 a piece a few years ago.
I started knifemaking using old sawblades but once I started using gauge plate I never looked back.
O1 is very easy to heat treat in the home workshop using nothing more than a map gas torch ($100 from Mitre 10) a few fire bricks, a few liters of canola oil and the kitchen oven for tempering.
Many of my early knives were heat treated with very basic equipment until I build a PID controlled electric furnace.
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