To reappraise is to estimate something's value again. An artist might be dismissed during her lifetime, but critics may reappraise her work years later and decide that she was a genius.
You can reappraise something for monetary worth, the way an antique dealer might price a chair at $100 and then reappraise it the following year (after oak becomes much more popular), raising the price to $1000. You can also reappraise, or reevaluate, qualities like your own self-esteem or your relationship with your siblings. When you appraise, you "set a value on" something. Add the "again" prefix re-, and you do it again.