Baseball America estimates that the Astros spent approximately $3.86m on international free agents in 2013, when they had almost $5m to spend.
The Rangers and Cubs each spent over $8m, and the Astros were (barely) outspent by the Dodgers, Indians, and Red Sox.
Now, as BA says:
The timeframe overlaps multiple signing periods, including the second
half of the 2012-13 signing period in which Major League Baseball gave
every team a $2.9 million bonus pool, as well as the 2013-14 signing
period, which began on July 2 last year and had teams begin with tiered pool spaces based on reverse order of major league winning percentage from the previous season.
And let's not forget that the Astros figure doesn't include the Pool Space for Ronald Torreyes trade, nor does it include however much the Astros spent on Japhet Amador and Leo Heras.