Another very interesting article by Richard Beedall, which I orginally posted on the Sea Jet thread -
MASC.
If the main options are Merlin, Osprey or Hawkeye, and cost rules out the the non helicopter options, then why not consider using a larger helicopter - say a Chinook. I think I'm correct in saying that it has a higher service ceiling than Merlin (even with stub wings), hence a greater radar range, and more room for equipment and crew.
Or am I just being dumb?