CC,
I believe the original figure is confidential, not sure if a FOIA request would reveal much here, but IIRC, it was "under €10m".
Either way, TUI will certainly get a good ROI, and questions were certainly asked at the time about whether the original deal was properly scrutinised.
IMHO, AA / CCC were backed into a corner, and TUI had the cash to bail them out. If it was a fire sale, then I would point the finger, as usual, at Warwick District Council. They have cost their own tax payers a fortune, and indirectly cost us here in Coventry too, not tot mention having the cheek of now trying to ask central government to bail them out.
AP, to take your argument further, you could also say that BHX will always have stringent noise restrictions, and limited use of said second (parallel) runway, not to mention the taxiing times.
So to take it to its ultimate conclusion, why not spend just another £5bn or so more, and close both Brum and Cov to build a new airport near Rugby?