Ballpark Figure

A ballpark figure is better than a wild guess, but not quite a "good as gold" estimate. In that vein, a ballpark figure is a rough estimate off the top of your head based on anecdotal knowledge, versus in-depth research. Ballpark figures are commonly used by salespersons and other quasi-professionals as a starting point in a negotiation. That is, the guess won't land exactly on third base, but it'll be in the ballpark.

For example: "John what do you suppose those three lots would cost?" "Ballpark figure would be $20,000 a piece."

Accountants aren't known for tossing out ballpark figures as much as they are known for being fastidious about being correct.