White vinegar you get at the supermarket is food grade, so won't contain anything harmful to humans (probably nothing harmful to film, either). It's generally distilled acetic acid diluted with pure water to 5% acidity; dilute 1+3 from that strength with water and it'll pass for stop bath (though without an indicator, you might want to one-shot it).
Indicator stop bath is actually cheaper, because it lasts and you can tell when it's gone off (the indicator turns blue/purple, looks black under safelight), so you can use it up before you dump it. I went cheaper than that; bought a bottle of 75% strength acetic acid (cleaning supply) on Amazon and sourced a little bottle of bromocresol purple (also on Amazon), which is the indicator used in the commercial variety. When the bottle I had in my storage since 2007 finally turns color, I'll mix mine to correct strength and add enough indicator to give it the right color, and probably use it for another couple years (for film; paper carries over a lot more developer and the alkalinity kills the stop bath eventually).