£500/600 would get everything with a brand new chip...

But you will need a breather kit for stage 3 and a rolling road tune

Look in parts for sale and get
Greens
3 bar mapp sensor
Breather kit
And a decent cooler

And get a new chip too suit and also check the fuel pump wiring and the voltage because they cause problems too

320bhp t3 and will drive really nice