underspend

from WordNet (r) 3.0 (2006)

underspend
    v 1: spend less than the whole of (a budget, for example) [ant:
         {overspend}]
    2: spend at less than the normal rate [ant: {overspend}]

from The Collaborative International Dictionary of English v.0.48

Underspend \Un`der*spend"\, v. t.
   To spend less than.
   [1913 Webster]

[email protected]