If you babies diapers don't hold it all during the night, try adding a budget sanitary pad in, sure saves on the laundry, not to mention making it a lot more pleasant for your little one.
On the same line, you can buy diaper liners rather inexpensively. The only place I can find them around here is Food Lion (no Wal-Mart or Target...surprise!) for less than $2.50 for enough to last a month.