If you love Little Greene Mister David but not the price, Dulux Spring Breeze 1 is the one to go for. It comes in at ΔE 2.2 from the original — that's a *very close* match, the sort of difference you'd struggle to spot once it's on four walls and the light's moving through the room. It sits at LRV 58.8, so it reads as a soft, sunny mid-yellow rather than anything heavy or acidic. For a budget swap, that's about as good as it gets.
Be wary of the other so-called alternatives floating about. Crown Mustard Jar is ΔE 8.7 away — you'd genuinely notice that side by side, it pulls warmer and more ochre. And COAT House Points is ΔE 13.2 off, which isn't a Mister David match at all; it's simply a different yellow. I'd not pretend either of those is the same colour.
Now the honest caveat: a cheaper paint isn't only about the colour reading right. Little Greene's depth comes partly from pigment load and the way the finish handles light — their Intelligent Matt in particular has a lovely soft chalkiness. Dulux Heritage is the closest Dulux family in terms of pigment richness if you want to spend a notch up from standard Dulux, but standard Dulux trade-grade emulsion in Spring Breeze 1 will do the job perfectly well for most rooms.
Practical advice: don't buy on the swatch number alone. Get a tester of Spring Breeze 1, paint two coats on a bit of lining paper or board (never straight onto a patchy wall), and move it round the room over a full day. Yellows are notorious for going green in north light and brash in strong sun. Check it where it'll actually live before you commit to the bigger tin. Do that and you'll save a fair bit without losing the look.