decided to give this a go wrxtasy

i am currently having my 97 sti ra rebuilt at asg and am debating whether it's the appropriate time to strengthen the box and/or getting an idea of figures associated with getting it done along with the most appropriate option...[went through a pile of websites, decided.. then went back to step 1]. Only thing.. I would rather spend less than 6k... a lot cheaper would be even better

driving style : i do a lot of highway kms per week[around 800], plus about 200km normal city driving.
i don't have a heavy foot, but i do push it through the gears hard every so often when the situation arises.

this car will go to the plex a few times just for a bit of fun. it will also be used for a bit of track use as well at wanneroo. most importantly though, i just want the assurance that i won't kill it if i give it bit of stick here and there.

while the engine is getting run in, the car will be babied... right after that, watch out, i want to see what it can do

power the box will need to handle?... well, i'd just like for it to be able to handle around 400-450 horses if i continue to modify, so let's use that as a guide.

any help appreciated.