How to format a US currency string using python or sed

I have numerous invoices that I sent to clients with this string at the bottom: Total: 1,000.00 or whatever the amount. Some are 2 figures, some 5 figures + the decimal part.

The thing is that the number's format is inconsistant accross all invoices. Sometimes its 1.000,00 and it keeps on switching the dot and the coma.

so with grep, awk and sed, i am able to only get the amount part from all invoices, without the dollar sign in order to sum them up to a grand total. But the dot and coma switching confuses python, obviously.

So in python (could be in sed as well), i am looking to convert the third char from the right to a dot and then from there on, every fourth char it finds, convert it to a coma.

In other words, it has to be able to separate the digits in groups of 3 from the right, add a coma in between each of them except for the first group at the far right which would be 2 digits separated by a dot.

Hope that is clear enough...

via Chebli Mohamed