The question which the comparison with airliner prices really begs, IMHO, is whether we should continue the pursuit of the "perfect" aircraft, or whether we should behave more like smaller nations who buy their military aircraft "off of the peg" so to speak.
For well understood historical reasons, we in the UK have tended to seek "bespoke"solutions to our front line aircraft requirements, resulting in the MoD bearing considerable development and marketing risk with the inevitable attendant cost burden. No doubt defence contractors have been only too happy to encourage this, but the fundamental cause of the problem is the desire to specify bespoke solutions. Greater flexibility in terms of accepting solutions which are good rather than perfect could be considerably lees expensive, without necessarily compromising fitness for purpose in any meaningful way.