QUOTE(Boris Cain @ Apr 5 2013, 12:46 PM)
If you give a ballpark figure or a ballpark estimate, you give a number which you think is fairly close to the actual one.
• We don't know the exact cost, but a ballpark figure would be around six million dollars.
• I know you can't tell me exactly when it'll be finished, but can you give me a ballpark estimate?
Ballpark estimate is an approximation, made with a degree of knowledge and confidence that the estimated figure falls within a reasonable range of values. Also called rough order of magnitude.