If you want Elephant's Breath without the Farrow & Ball price tag, Dulux Dusted Cappuccino is your colour. It sits at ΔE 1.2 from the original, which is well inside the "can't tell them apart on the wall" range — anything under 1 is genuinely imperceptible, and 1.2 is close enough that no one's going to clock the difference once it's up and dry. Its LRV of 54.3 keeps it in the same soft, light-but-not-stark territory that makes Elephant's Breath so easy to live with.
Second choice is Dulux Knotted Twine, at ΔE 1.6 and LRV 55. Still a very close match, just a fraction off Dusted Cappuccino on the colour science. If your local stockist has Knotted Twine mixed and ready, it'll do the job nicely.
Now, the bit worth saying out loud: Elephant's Breath is one of those F&B colours that shifts with the light. It reads warm greige in a south-facing room and can throw a faint mauve-pink in cooler northern light. A Dulux match nails the colour, but it won't have F&B's chalky estate-finish depth — the way the pigment sits and shifts is part of what you pay for with Farrow & Ball. For a feature wall or a room you really care about, that texture matters. For a hallway, a rental, or a big space where budget rules, the Dulux match is a cracking call.
Practical advice: get Dusted Cappuccino as a tester first and paint a decent-sized patch — at least A3 — on more than one wall. Live with it across a full day before you commit. Match it in Dulux Diamond Matt for high-traffic areas, or their standard matt emulsion for ceilings and quieter rooms. Don't judge it from the tin lid, and don't judge it under a single bulb at night, mate. Daylight is the only honest test.