homemade developer - instant coffee & washing soda (sodium carbonate)
homemade fix - allegedly the "make water safe for fish" drops contains sodium thiosulphate so in a pinch you could use that MAYBE but it's way more costly than fix so few people have tried it. I know a 250ml bottle of Tetra Aquasafe costs about 8 and there's lots of other stuff in it so it's probably not at the right concentration either.
Edit: actually Tetra Aquasafe is one brand that DOESN'T contain Sodium thiosulphate apparently (when I googled)