Which ones are you talking about? The "pricey" ones usually are smaller series from smaller manufacturers produced in western countries, often made from more expensive materials (like eg hybrid wood).
With the chinese ones the main factors are 510, contacts and build quality of the enclosure. Remember when I said "if designed properly"? If the 510 isn't good it can leak, if the switch and contacts are bad the mod will hit like a cooked noodle wrapped in wet toilet paper. When your desire is a cheaper mech squonk I'd suggest the pulse or the hugo.
I doubt you can make a good quality squonk for 12$. Better to pay the extra 15$-20$ now than pay 12$ now and 30$ later.
