No you are not bonded and yes you do have to pay £21K from your salary (even if you are PPY) however I believe the cost is taken before tax and NI and over a 3 year period. Or you can elect to pay £2400 per month for the first 8 months of service, which comes to £19200.
So for a no-jet-time with over 1500TT, year 1 (and perhaps 2...) is spent on less than 2K/month net, possibly based in LGW? Oh dear...
looking at the "bright" side, it still beats P2F I guess.
DK