Well the NSA claims (I'll stipulate "claims" as it's not as if I could check anyways) that they only hold it for 5 years.
Congress could enforce the matter by just not giving them money to build anything fancier though. Even the NSA has to obey information theory and physics.
Unless I am mistaken, that is only for a specific subset of data. The released policy also includes indefinite retention of encrypted data, even on Americans.
As far as budgets are concerned, when is the last time anything in the intelligence budgets was significantly cut that it affected their operating capabilities?
Good luck asking the spying industrial complex to hold on to your data "for a limited time only".