Here's Apple's official AppleScript reference:
http://developer.apple.com/documenta...SLR_intro.html
I actually find Matt Neuberg's book AppleScript:The Definitive Guide (O'Reilly) more helpful.
Here's an example of an AppleScript that does approximately what I described above:
Code:
tell application "OmniPlan"
repeat with t in tasks of front document
if task type of t is standard task then
-- effort is in seconds
set budgetHours to (effort of t) / 3600
set budgetPrice to value of custom data entry "Budget Hour Price" of t
if budgetHours is missing value or budgetPrice is missing value then
set budgetTotal to 0
else
set budgetTotal to budgetHours * budgetPrice
end if
set value of custom data entry "Budget Total" of t to budgetTotal
end if
end repeat
end tell