Question : Is there another local airport that can get you to London?
Answer : Departing from Orio al Serio International Airport is not the only way to get to London Heathrow Airport. Try looking for flights from Milano Linate Airport (LIN) as well. Over the next few months, flights from LIN to LHR are being booked 40% cheaper than flights from BGY to LHR. Being only 25 miles away, it's easily accessible for most.
Question : How long do most people stay in London?
Answer : Of course you're not most people, but if you were, you'd stay roughly four days.
Question : Would you be willing to change your travel days if it saved you money?
Answer : In March, Saturday is your lowest-cost day to fly. Having flexibility in your travel plans means you can save more, so be sure to plan ahead when possible.