I've only been to Luton airport once and that was many, many years ago. Since there were 4 of us sharing a taxi, the cost wasn't too bad. From what I remember the airport was a pretty dingy place and it seemed to cater to charter flights (we were flying to Athens). Maybe it has had a facelift - as I said, it was many years ago.

I checked the internet and they have a website which has a blurb about getting to London. The site is: http://www.london-luton.com/body4.asp

Enjoy your trip

Marty