Perhaps instead of mocking his guess, you could provide the answer? I am just curious because you mentioned maybe using metal, but in those images I dont see much metal. You also mentioned you had received quotes, which means you have an idea of the construction.
I realise all this may be in the air as well, due to your hesitation to nail a price on this. But instead of trying to hit the magical number on the head of 'cost' to 'effort you want to put in' ratio- perhaps you could create alternate schemes with pricings, and we on the board could tell you which seems most appealing to us. eh?