bmibaby generally have higher fares than Easyjet. Easyjet fly to three different London airports, which all have good, cheap rail links with the capital. East Mids doesn't even have its own station - you have to get a bus to Loughborough. And yes, getting a train the 100 miles from Loughborough to London would cost more than the short journey from Luton or Gatwick to the centre of London.
Honestly, I can't see any reason not to just use Easyjet to fly to Luton or Gatwick (for preference) and hop in on the train. Unless for some reason the fares are extremely high, but I can't imagine that they would be high for Easyjet and not then high for everyone else.