decat/Sports Cat £100/£300
could always get bigger injectors and a bigger intercooler and possibly a bigger turbo but thats over budget, and probably not worth it!
No cat issues on a DCI.
BIgger injectors well forget it there custom stuff so £1k there maybe or the 100 setup which need the new pump and cambelt as well doing and for the gains not realy worth it.
DCI 100 intercooler is the better cooler but unless your running extreme windows and maps no realy need.
Bigger turbos only needed if you'e the injectors or you've pushed youtr stock injectors massive windows sizing.
IMO my mods would be
H and R coilovers £750 I think
Decient Tyres
Save the rest for the brakes when you do chnage them bleed the fluid for decient new stuff new pads (stock are more then enough) and new disks.
But if I had £1k would be spent on track days etc on the stock car way more fun.