You seem to be missing a key fact here, MRA4 was months away from service and would have cost the tax payer nothing more, scrapping it cost another £200 million....how is that cost effective?
I believe the savings quoted are the through-life operating costs.
BTW, I'm not agreeing with GrahamO, his type of ill-informed opinion is of no relevance as his knowledge of the facts is at error and his tainted opinions of the MoD (RAF) procurement process are clear, though I do tend to agree that it was a tad expensive. Doesn't take away from the illogicality of cutting it just as all that investment was coming to fruition.