After trying out a bunch of checkbook apps that were both pricy and had too many features compared to what I needed, I decided that I could do it in TaskPaper.
To use this. Just make tasks with the format "Entry name: Amount" (like "Groceries: -30.80"). Then select the tasks you want to total and run this script:
on splitText(delimiter, someText)
set prevTIDs to AppleScript's text item delimiters
set AppleScript's text item delimiters to delimiter
set output to text items of someText
set AppleScript's text item delimiters to prevTIDs
return output
end splitText
tell application "TaskPaper"
set selected_entries to get selected entries
set total to 0
repeat with each_task in selected_entries
tell each_task
if entry type of each_task is task type then
set theContent to text content of each_task
set thelist to my splitText(":", theContent)
set amount to item 2 of thelist
set total to total + amount
end if
end tell
end repeat
end tell
display dialog total
The script adds up all of the amounts that you have highlighted (it ignores project and note lines) and displays a box with the total.
