Of course, more funding would be welcome. It is also dangerous. Anyone who has read an appropriations bill knows that most funding allocations are for broad categories of expenses, such as salaries. It is not congressional practice to appropriate money for the enforcement of specific laws. Neither Congress nor agencies would welcome that type of micromanagement.
Many laws impose general requirements on agencies.
The agencies themselves have to allocate funds for these responsibilities. FOIA must compete with other activities for funds. A specific line item for FOIA could actually work against the law. Once the funding ran out, the agency could then shut down its operations for the rest of the year. Congress can pressure agencies to do better through oversight and hearings.