Worth noting the ED30 gets the S3 shifter as standard.
I think you've covered most of the cheapest improvements
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A VIS pump is a good idea too, and although it's 2.5x your budget, it's far better value than the other choices.
I agree the handling is where the investment is better spent, but that's where things can get properly expensive, depending on requirements, but anti-roll bars aren't THAT expensive for the improvements they give. Especially compared to the very poor performance per £ value of 2+ hardware.