Universal standard dollar
The universal standard dollar (USD or $) – sometimes also referred to as the Nationstates standard dollar (NSD) or Multiversal standard dollar – is a hypothetical currency that is used as a common reference point for international transactions, such as football transfers. It is not linked to any specific currency or commodity.
As a rough guide however, a transfer fee of $1 million is possible for a football player in the prime of their career playing for an average-ranked national team. This sum is also roughly the entire annual transfer budget for a single club in a league new to IFCF competition.
Nationstates does provide players with a GDP figure for their nation(s), and some tools exist to calculate an exchange rate from this figure into an equivalent "standard" universal currency, which may then be used as a basis for a nation's in-context perception of universal standard dollars. For example, a nation with a poor exchange rate (as calculated by one of these tools; based on the strength of the national economy according to Nationstates' underlying values) may consider a fee of $1 million for a footballer to be an outrageous, nigh-unaffordable sum. For a nation with a stronger economy and better exchange rate, this fee may represent a pittance.
It is important to note, however, that many nations' decisions on how to roleplay USD is not necessarily linked to their nations' in-game metrics.