I would say for that budget you will be able to source a nice STi in the age bracket you are looking for.
The important thing would be knowing as much of the history as possible as with a car 10-15yrs old - it will probably have seen a few owners so checking cam belts being done, regular oil changes, things like that will help.
10yrs old car will give you an STi Blobeye - any older and you will be looking at a Bugeye
See which you prefer the look of, and hope to see you in a scoob soon
Ryan