Let's be straight: Marine Blue is a deep, properly saturated teal-blue, and that depth of pigment is exactly what makes a cheap match tricky. The colour leans dark and rich, so any alternative needs serious pigment load to land in the same place — and that's where budget paints often fall short.
The nearest of the bunch is Dulux Azure Fusion 1 (LRV 5.4) at ΔE 6.5 from the original. That's not a true match — anything under ΔE 2.5 is what I'd call "very close" — but it's the best of what's available at a lower price point, and side by side most people wouldn't clock the difference on a wall. If budget is the priority, that's where I'd point you.
COAT's The Drink (LRV 7.4) comes in at ΔE 9.4, and Crown Endeavour (LRV 9.8) at ΔE 11.2. Both are noticeably lighter and shifted in hue — they read as their own colours rather than dupes of Marine Blue. Lovely shades in their own right, but if you're chasing *this specific* teal you'll be disappointed.
Here's the honest bit: with deep colours like this, the difference between Marine Blue and a near-match shows up most in how the pigment behaves under different light. Little Greene's Intelligent and Absolute Matt finishes give Marine Blue a real density and even sheen that cheaper paints can struggle to replicate, especially on a single coat. You may save on the tin but spend it back in extra coats and a slightly flatter, less resolved look.
My advice: if Marine Blue is the hero colour in the room — a dining room, a bold hallway, a feature wall — pay for the real thing. It's not a colour where you want to compromise. If it's a cupboard interior, a utility, or somewhere the light is forgiving, Azure Fusion 1 will do you proud for less.
Buy a sample pot of both and test in situ before you commit — a tester is always cheaper than a wrong wall.