Hi, I understand your point about costs,but you could have got a decent quantum 400 or similar for the cost of your bag. Similarly, your downmat must be the dearest mat one can buy.
As for noisy neoairs I don't find it a problem, but even so, the simplest solution for a good sleep in a tent is always earplugs.
As for punctures, I'm more concerned about the ground sheet of my ??300 tent than my mat.