I wouldn't normally do it this way, but there is an "Etc." column on this spreadsheet for the 2 or 3 odd values that don't belong in any of the other columns. It is bad enough, presentation-wise to have this column, I didn't want to introduce yet another column to keep the comments separate, even though that's the right way to do it, in terms of spreadsheet integrity.
The values are [Dollar amount][CR][Description]. such as the one I'd mentioned earlier:
$250,000
(I & B)
Your formula would have worked if every cell contained a number and a CR. I entered the following unwieldy but functional variation on your formula to avoid the dreaded #VALUE!:
{=SUM(IF(ISERR(VALUE(LEFT(I4:I45,SEARCH(CHAR(10),I4:I45)-1))),0,VALUE(LEFT(I4:I45,SEARCH(CHAR(10),I4:I45)-1))))}
Do you have a more elegant solution?