I just thought I'd mention the Wilkinson WV-PC Stratocaster replacement tremolo system as there are often discussions here about budget guitars and what needs to be changed to make them much better. I've used the vintage style Wilkinson trem before and I know they are excellent, as well as the more expensive VS-100 that I have also.
I decided that my SX Strat that cost me £80 on eBay would benefit from a change too, as the trem was flimsy and my usual cure of PTFE tape didn't give me the same satisfaction as with Fender models. I took a chance and went for the 'pop in' style with a soft aluminium surround and I'm pleased that I did. It cost under £40 and feels absolutely amazing to play, with it's solid steel high mass block and smooth edges. My VS-100 is fabulous too, but costs £60 more. Therefore if anybody need a recommendation for the lesser known WV-PC model, I can tell you it's absolutely amazing and feels it should cost five times it's actual price.
I also fitted a set of Mojo Vintage Strat pickups that I found on eBay last year and they are amazing too, but not cheap to buy new. This modest SX standard Strat now feels and plays as good as any of my £2000 + Fender Strats.