Did you just compare the cost of a 145 R12 tire to the cost of a 195/65 R15 tire? those are over 3" taller and 2" wider then a 145 R12.
In case I am missing something, you can get some low rolling resistance tires in that size for $75 each,
Tire Search Results
Or if you are looking for something that will kind of fit your geo metro, altho still to big you can get some 175/70 R13 LRR tires for $57 each at just over an inch wider then stock and over an inch taller.
Kumho eco Solus HM KR22
or the 165/65R14 tires that the Insight uses for $87 each, altho they are still an inch taller then your stock tire and 3/4" wider then your stock tire.
But if you really do want something that is the stock size for your Geo Metro, try finding a Zenn neighbor hood electric vehicle dealer or other NEV dealers and get some tires from them, nice quite, LRR tires in 12" and 13" sizes.