I'm trying to remember what the difference in insurance was it was not as much as I was expecting. I pay monthly and it was about 7 pounds a month more so 85 quid a year which for the difference in performance is very little to pay!
Bear in mind as well even though the WRX only has 30bhp more than the Celica the difference in torque (230 vs 133) makes it a completely different animal so you won't be wanting more power for a while and when you do you can get mods to take it to 280bhp relatively cheaply - remap, filter and wxhaust upgrade