Well it's our local decorators that's being going for decades and has always been competetively priced. I have to admit this is extra tough paint (hallway with 3 kids. NISM?) and a specific colour but was £40 for the standard stuff and even that's nearly twice the price I was expecting.
Older and more confused than I could ever imagine possible.
Try Lidl! I always buy white - and mix up the colour myself (after painting the ceiling) by adding small amounts of old coloured paint - or tints where required. Just make sure you mix enough!!