I don't know what boat it is, if you could get a picture from the side showing the whole length, someone might know.
Looks like a 2x4 internal support for the forms and possibly commercially made forms?
Plans, forms, and the internal support would cost between $150 and $200.
If he cut the strips himself, the wood for the strips was probably about $70.

How long is the boat?

Generally there should be plans in the possession of the widow. People would want them to finish the boat.

Personally I might pay $150 with the plans. A lot would depend upon the quality of the stripping.
Is there any fiberglass or epoxy with the boat? Those are two of the bigger expenses in the build.