I started swapping labor camps at 1999.99 infra. If you extend your collections then improvement swapping can be profitable. Swapping labor camps for factories then banks then labor camps again cost 2mil. At 1999.99 infra, infra upkeep bills are approx. $500k per day (approx due to trades and tech levels). So if you extend your collections past 8 days, improvement swapping becomes profitable.