A bad mod/dollar is the AFE takeda intake. I purchased it for 250 brand new from a guy at a local BRZ meet. Installed it. It gave more low end torque but the torque dip is way way way more
I can't wait to get my Perrin headerback and stage 2 tune after my first service. I kinda regret buying the intake over a K&N drop in filter that adds 5hp for $45, when the AFE takeda probably adds 7hp untuned for $250.
Best mod/dollar is the whiteline brace and perrin bushings. For 80 bucks, you get a solid, firm, nice, positive shift experience. It's so rewarding and brings on so many endorphines when you drive.