Hi Stephanie,
What is the formula in G130?
Values in column G121 to G123 are centred in the cell.
What happens when you change the alignment to Automatic?
I suspect Numbers is not recognizing the "colones"symbol as a currency symbol, and is treating the column G values as Text, rather than a number representing an amount of currency.
"copy and pasted from my statements" could also be a factor.
All 'text' values have a numeric zero value when picked up by a formula, so the 'sum' in G130 is correct if the values in G121-G123 are all read as text.
Steps to take:
Select column G.
Click the Format brush,
Click Text.
In the alignment bar,
Check the current setting.

Click on the "A" button (Automatic) and observe the behaviour of the three values.
Data recognized as Numbers, including currency, will align to the right. Text values will align to the left.
Actions:
Change the Data Format in cells that have or will have these numbers to Currency.
If the sums stay at zero, the currency sign is not being recognized, and you'll need to remove it to get a sum.
Whether or not the colones is available in the list of recognized symbols likely depends on the region setting you've chosen. If it is available, you'll find it in a pop up list in the Currency page of the Format Inspector.
Regards,
Barry