I would not despair too much, there are more options available than a £3000 Plus rebuild, especially considering the age of the car.
Firstly, is your car is a 'WRX' RA and not an STI RA (Does it have DCCD for instance) as this will dictate if you need an UK/WRX spec bottonm end or the stronger STI spec one.
There are always people uprating their bottome ends for forged/steel ones or even 2.5 upgrades out of choice, rather then neccesity. A quick ceck on SN, will find you a couple at least that you can buy and have someone fit for you.
Alternatively Essex Scooby breakers will supply and fit a second hand engine complete, out of a car they have bougth accident damaged. Admittedly this may be a risk, but the last person I suggested this to spent less than £1200, including a TDO5 upgrade on his MY95 uk car. (Dont forget you can effectively get a cheap cambelt change/service too!) He has had no problems since.
OK, so £3-4K will give you peice of mind for the next 4 years, but how long are you keeping the car, and will £1k mean you can STILL keep it for two years?