I wouldn't say that parts are any cheaper. All of the engine/carb/gearbox costs will be the same no matter what you drive. Front beam and steering should also be the same. The only real difference between cars is track rods, trailing arms, pushrods, etc... These don't cost much and can be made by your local workshop. After that each builder has different suspension layouts which should all cost about the same.
I do know that replacement nosecones for the Ray are about three times as expensive as a Sheane nosecone.
You might consider both the Irish chassis - Sheane and Leastone - because of the advantagous sterling/euro rate. Both have good history and both have their merits. The Sheane would probably work out cheaper. I know that I went quicker in a Leastone. Check out Alan Harding at
www.formulavee.co.uk and he can organise a test in both (he can also sell both to you).
Let me know if you get a price for Sheane/Leastone. I should be able to buy one in Ireland a lot cheaper and we could do a deal for cheaper than you'll buy in the UK (approx GBP£4350 brand new rolling chassis less engine).