The national average for mileage is thought to be around 12,000 to 15,000 miles a year. http://www.fhwa.dot.gov/ohim/onh00/bar8.htm
So even on the high side at 15,000 you are looking at 165,000 for an Model Year '02. That being said, you can and will find cars higher than that mileage and still be great condition, or lower and worse. As for price, check kbb.com for your area and remember that modifications to the car generally lower the amount it is worth. I did a quick search of '02 WRX's on Cars.com and found prices from $4,000 to $14,000, with varying mileages and conditions.
I hope you find the one you want and more importantly, can afford it. Good luck and welcome.