Question About the Envelope (Likely Spoilers)

After discovering her preggo situation, Sophie knocked on the door of the sperm donor's apartment and told him "mission accomplished" then handed him a small envelope which presumably contained his $30K bonus. The envelope seemed a bit small to contain the amount of cash described. Also for the wife, it would seem hard to manage large amounts of cash without the husband or feds getting interested.

He killed sixteen Czechoslovakians. Guy was an interior decorator.