  We study the fair division of a collection of $m$ indivisible goods amongst a
set of $n$ agents. Whilst envy-free allocations typically do not exist in the
indivisible goods setting, envy-freeness can be achieved if some amount of a
divisible good (money) is introduced. Specifically, Halpern and Shah (SAGT
2019, pp.374-389) showed that, given additive valuation functions where the
marginal value of each item is at most one dollar for each agent, there always
exists an envy-free allocation requiring a subsidy of at most $(n-1)\cdot m$
dollars. The authors also conjectured that a subsidy of $n-1$ dollars is
sufficient for additive valuations. We prove this conjecture. In fact, a
subsidy of at most one dollar per agent is sufficient to guarantee the
existence of an envy-free allocation. Further, we prove that for general
monotonic valuation functions an envy-free allocation always exists with a
subsidy of at most $2(n-1)$ dollars per agent. In particular, the total subsidy
required for monotonic valuations is independent of the number of items.
