I have experience of two of those basses - the Integra and the Corty. Both great basses. The other two both have good reputations. I now play a Shuker - not because I'm such a great player, but what I wanted didn't exist, and it was a lovely way of having something from the very modest amount my mum left me.
Difference between them? The same as the difference between supermarket Champagne and Dom Pergignon. Only ever had Dom Perignon twice and that was when someone else was paying. It is crazy expensive, and yes, you can tell the difference, but the more you pay, the more marginal the improvements become. And to be honest, until I gave up drinking I was always happy drinking supermarket Champagne, but will always remember the DP!
As for other sub £500 basses, Ibanez (although I don't like the open pore necks on a lot of them), G&L Tribute (made by Cort) and even cheaper, Revelation.