Looked at the plain blue version of this in Asda Living and the more expensive models in Halfords - the difference is the padding thickness and colour. If you can live with the plain blue of the basis model then you can get it for £40 or less. This is eactly the same as the £90 otherwise! We have the cheap one and it's completely fine.
Also note that Halfords have this on sale often - they rotate offers, seems to go one month for the Graco, one month for another brand.
Great car seat, I have two one for each car for my son. Asda are selling it on offer at the moment for £25.