GTA Money. Due to massive inflation in the online mode, a pair of shoes costs $10,000 dollars. You see, Los Santos was clearly just in the middle of a Great Depression. Then, the U.S. stepped into a war and brought on the Mobilization Economy. Now, the economy and farmers are doing swell. Causing prices to go up due to overproducing and consumerism.
[spoiler]In all honesty though, probably Rupees. Its just really nostalgic.[/spoiler]