In keeping with the spirit of the challenge, I'm trying to use reclaimed parts where possible and the cost savings are enormous.
Lets take the tanks as an example: To get a tank made up from scratch (two parts formed then welded together) would have first involved the making of a stamp tool at a cost of around £2.5K. Although I could then have had an unlimited number of tanks made, for small volumes (<1000) they would have worked out at around £70 each if the tool cost wasn't amortised in the price.
The alternative was to take a trip to Asda (other supermarkets are available!) and buy two 450psi 'Happy Time' helium cannisters complete with balloons. Helium is a scarce resource so we waited until a couple of birthday parties had passed before I could get to grips with them. The cost of the two tanks, helium and balloons was a grand total of £60 so as Richard would say - QED. Some drilling, welding, brazing, plumbing fixtures and painting later and I have my engine test tanks.
I'm adopting the same strategy with as much of the mechanics I can, and ScrewFix and eBay have become my new best friends. Even the combustion chambers of the engines themselves are made from ex CO2/Argon gas cannisters with some bespoke engineering for the throat and nozzles. The fuel filters are heating oil filters, the actuated valves are made from standard plumbing fitments coupled with high-torque radio control servos, the ignition coils are from 2 Ford Focuses etc. etc.
Of course its not always possible to use existing kit - the engine test stand is made from scratch, as is all of the electronics - but I've found you certainly don't need to keep on reinventing the wheel as kit with the specs needed is already there. This may seem obvious, but its come as a bit of a revalation to me.
Sorry, I appear to have gone on a bit. More photos soon.