I once sold three very heavily modified but equipment-stripped AS355s for what seemed a pittance as they had additional brackets, holes, miles of extra wiring (even on a 355) and horrid bumps all over them.
The buyer took them all and did some work on them. They sold them later for a 2000% profit and even the last operator got a great deal out of it.
Dont get caught up in selling the whole package, ITAR bits can be removed.
Sentinels may be worth a lot more as straight airframes if money is important. I remember that, when Laarbruch closed, a local farmer bought a strong cabinet for DM150 in a disposal auction. Inside the cabinet was £6M worth of Harrier test equipment that no-one wanted...