I have a WR Blue BRZ:
My first mod cost me $0.40 and involves zip ties:
My second mod (factory fog lights) was free because of a clerical error by the dealer on the paperwork:
My latest mod cost $13 total, $9.75 at home depot for vent magnets, and $3.25 for a new pack of xacto blades:
Grand total spent on my awesome mods: $13.40ish. I dare anyone else to beat that.