Any good deals on laundry detergent?

Could someone tell me what is the current best value on laundry detergent?

The last one we had here was a big box of Daz which must have lasted about six months.

I'm not a fan of Alid/Lidl laundry detergents. And I prefer powder over liquid. Had a look in a shop today, but I found it hard to compare brands as there are so many different sizes.

Looking at Tesco, I see these deals:

Ariel Washing Powder 2.6Kg 40 Washes €7.49 (€2.89/kg)
Persil Biological Washing Powder 45 Wash 3.185kg €9.00 (€2.83/kg)
Persil Non-Bio Washing Powder 45 Wash 3.185kg €9.00 (€2.83/kg)

And not on sale, but about the same price:
Tesco Ambience Laundry Powder Lavender 2Kg €6.19 (€3.10/kg)

Then in the pound shop, bigger packs but not any cheaper than the Tesco specials:
Persil Non-Bio Washing Powder 90 Wash 5.525kg €19.99 (€3.62/kg)
Daz Washing Powder 4.225kg €15.99 (€3.78/kg)

Any info would be greatly appreciated.