Digital BW, The Print

If this is a real fluid mounted drum scan, there should be no difference 
at all in the cost for these resolutions, so there's no reason not to go 
for the 300 ppi scan. As others have mentioned, the ultimate quality of 
the scan has far more to do with many factors not related to resolution 
and those things are what you should be shopping for. Buying scans by 
resolution is like buying a car by horsepower or an audio system by 
watts.

----- Original Message ----- 
From: "ag000002002"
For a 12x18 print, the service bureau offers:

100 dpi (1200x1800) which is a 6 MB file;
200 dpi (2400x3600) which is a 25 MB file; and
300 dpi (3600x5400) which is a 56 mb file.