2nd stage car seats?

[hercules]

Does it have to be a really expensive one or are the cheaper ones just as good?

I got a Britax one for £120 from a local small business who tested several in my car to see which fitted best. The one for my mum's car was £100 from the same shop. These may be more expensive than some of the others because of a recline feature on them (really handy for whan dd needs a nap) but they weren't the most expensive.
I think that fit is what dictates price as the £100 one wouldn't fit my car