Hi Chris the cost of the mould and resins I use is not that costly, for 1kg of Rubber and 2kg of resin, plus postage is around 52£. This will easily cover my needs in make all the fittings for this project and a couple of others.
If you and your friends are say making the same scale subject , like say 1/72 British warships the door, locker etc are the same, so you only need to make one mould that can used by You and your boaty friends.
One rule I never break is NOT TO COPY manufactures fitting, this to me is a massive NO,NO, and why I alway keep my masters so if I was ever asked to prove I had not copied fittings, I can show My masters and the moulds.
The supplier I use is CFS in Cornwall, I know there are other suppliers out there that Modellers here use, however there product has works well for me over the years.