Assistance Anyone?

I may have the opportunity to be in London for the Chelsea-Arsenal match Sunday Nov. 30 and I clearly would love to head to Stamford Bridge for the match. Having never been to London, much less Stamford Bridge, anyone have any advice as far as getting tickets?

• Where's the best (safest) place to get them online?
• How much should I expect to pay?
• Is it possible to walk up and get a ticket the day of the game?
  

Any help is much appreciated. Either leave me a comment or shoot me an email.

Thanks