Chantilly Lace is one of the cleanest, brightest whites going — a true crisp white with very little undertone, which is exactly why people love it and exactly why it's a pain to swap out. Most "white" alternatives lean warm or grey the second you put them next to it. But you've got genuinely good options.
Dulux White Cotton is the standout. At ΔE 0.5 from the original it's imperceptibly different — you would not be able to tell them apart on a wall. LRV 87.6 keeps it just as bright and bouncy. Dulux is widely stocked, mixable at any merchant, and noticeably cheaper per litre. If price is the whole point of the question, this is your answer, mate.
COAT's Cat's Cradle (ΔE 0.8, LRV 85.2) is the one I'd point you to if you also care about low-VOC, water-based paint with a flat-matt finish that brushes beautifully. It's not the cheapest on the list but it's better value than Benjamin Moore and a lovely paint to live with.
Crown Swan Feather (ΔE 1.3, LRV 84.1) is still a very close match and another budget-friendly route if your merchant stocks Crown over Dulux.
The "but what about" here: don't assume a match on paper means a match on your wall. Chantilly Lace's brightness comes partly from Benjamin Moore's particular base and pigment load. White Cotton is the closest formula, but always test the alternative in the actual room, on a few walls, in daylight and at night, before you commit a whole house to it. North-facing rooms will pull any bright white slightly cooler.
Practical advice: order a sample pot of White Cotton, paint two coats onto a bit of lining paper, and tape it next to a Chantilly Lace sample if you can get one. If you can't tell them apart — and at ΔE 0.5 you very likely can't — go Dulux and pocket the difference.