Go to the area where Brucie is when he wants you to do the street racing mission (number 1 or something like that).

On that long street there always seems to be a bank truck.

Find one and take it to somewhere isolated then... blow it up.

Money will appear all around the truck so quickly pick it up before the cops come and get ya.

Or just do what I do and right after you blow up the truck use the lose wanted level cheat and then pick up the money.

Go quick though because the money disappears after like 30 seconds.