If DIY engine rebuild, which is dead easy I would say around £700 - £1100 roughly, depends a lot on what you find, £400 right away for new pistons for example.
To give you an idea my own engine is in bits at the mo after having done interstellar mileage of 200,000K, it has always had(with me) engine flush prior to every oil change.
Needs new pistons as expected but the crank only needs a polish on three journals, new pump needed, got new pinto pump £20, and upped the pressure, takes all of 1 minute!!.
Mine will be around the £700 mark with parts/machining cost.
The various stages usually concentrate on stage 1/2/3, stage 1 is mostly just a chip change for about 275bhp, stage 2 most don't bother with they go to stage 3 which is diffeent injectors called 803's or dark greens, chip, map sensor etc, above this mostly it's as much as you want to spend.
My advice is decide whether you want 2wd or 4wd, they are very different to drive at the limit esp, plus trans on 4wd is a lot weaker and costs serious money for big power due to this 4wd system.
tabetha