https://www.youtube.com/watch?v=WN_h9juITLk&t=320s
He gained 3.94 HP ($18 per HP) by adding a BMC air filter. Then he removed the airbox and added an EVO air intake and gained (not additional) 6.27 HP. ($60 per HP). It seems as though the BMC air filter is the better bang for your buck, but for these cars every HP you can squeeze out is better, for an additional 2.33 HP over the BMC, which would you do?