Speaking as someone who has commissioned repro parts on many occasions, I doubt the show of hands will sway you one way or another; there are simply too few cars to influence economy of scale.
The significant cost here will be the cost of making the tooling, once that exists, the cost per unit will not vary greatly however many are committed to. For example, with the seat diaphragms, the unit cost between runs of 50 and 100 varied by just shy of £1, so to save having to store them all we opted for an initial 50 knowing we could order a second 50 when required. Despite an initial show of hands for over 30, some two years on we are nowhere near needing to order a second 50 yet.
With the seat diaphragms, the nearside and offside are identical, so the 50 we bought weren't even car set pairs. With the 1/4 light seals, the car set is four individual components, but there will likely be greater demand for the fronts over rears, and I suspect greater still offside front over nearside front.
I'd suggest you seek a cost for the tooling, with the Club or whoever funds the cost taking ownership of the tool, and work out a unit cost based on say an initial run of 50 of each type to reach payback/break even once perhaps 30-35 of each have sold. As supplies of each type dwindle, more can be ordered.
Given the likely timescale between orders, I'd recommend that not only ownership, but also possession of the tools is negotiated, as if anything happens to the manufacturer, the tools would otherwise be lost. It also ensures exclusivity avoiding a scenario where the manufacturer starts selling direct, effectively able to undercut.
Seat diaphragms? I didn't know that these have been remanufactured? Can't see them on the TDC spares list?