Stansted bus to London..easybus or Terravision???

There is a train, the Stansted Express, which goes into Liverpool Street Station from whence you can go down to the Central Line Underground to Notting Hill tube station. Walk, cab, or bus from there depending.

The train is a lot cheaper than it used to be if you book it well in advance - £8 one way, so don't rule that out too. Comes into Liverpool Street so for Notting Hill you could take the central line from there. Neither of the main bus operators would get you into walking distance (Victoria / Baker Street) either, but they can be as cheap as £2 if you are lucky.

Another possibility would be to get the National Express bus or Terravision to Stratford and then the Central Line underground from there to Notting Hill. I've been very happy with National Express but have seen some very negative responses to Terravision.