I bought mine, same year but 84,000 miles, and it booked for and I paid $9,500. The GT engines have a timing chain instead of a belt like the GTS that would need replaced at 100k. Gen 7 Celicas have been known to go over 250k before they need any major maintenance done.
I paid 9500 and am very happy with the car, had it over a year and already put 25k on it myself.
If you end up getting it and want any information I found a FULL Toyota factory shop manual for Gen 7, it has 1800+ pages in a PDF and comes in two parts. I was going to buy the book but it was a few hundred $, so I was happy to find a download link for it
http://sharecash.org/download.php?file=1173281