Live Grand Exchange margins on the highest-volume items in Old School RuneScape — gems, ores, bars, runes, arrows, cannonballs — the staples that fill fast. Numbers below are pulled live and already have the 2% GE tax subtracted, so what you see is what you'd actually keep.
Items trading 100,000+ units a day fill orders almost instantly, so profit comes from turning capital over many times rather than waiting on a single fat spread. They're the lowest-risk way to flip: liquid enough that your offer competes with dozens of other traders instead of sitting alone.