In message , Sam writes

Could you please let me know the cheapest way from Hounslow or Victoria to
Gatwick / Stansted or Luton.

Hounslow is on the western outskirts of London, while Victoria is in the
centre - so your starting point will make a big difference.

The cheapest way from Victoria to all three airports (Gatwick, Stansted
or Luton) is by National Express coach. Go to ..

http://www.nationalexpress.com/ and then click on the "Airports" tab.

From Hounslow, you can get to Victoria easily by tube (take the
Piccadilly line and change to the District at Hammersmith). But you may
find it cheaper and quicker to go in the opposite direction from
Hounslow to Heathrow (only a short journey) since there are direct
National Express coach services from London Heathrow to all three other
airports that you mention.

While travelling by coach is cheap, do remember that the distances are
considerable and roads are often congested, so allow plenty of time.

--
Paul Terry