I’ve got the Joie elevate r129 car seat from Halfords £80 for my 18 month old goes up to 12 years and u can get one with isofix too but not a single complaint about it from me x
Another vote for the max safe pro! x
We have the max safe way pro is my partners car and I have the axkid minikid 2.0 for my car. Both great seats and got both for under £450
We have the Britax max safe pro (safe way m is very similar but cheaper version). It’s a very safe seat, highly tested, RF until 36kg and can be found for under £200. It’ll last her until she can go into a HBB. It does take up a lot of space but for the price it’s amazing. Axkid and besafe stretch are also very safe seats but they’re both lots of money!