Ars and i were just talkin about some good DIY setups recently.
The gun i was looking into has an LED temp readout and has a variable temp that goes in 10 degree increments. it ran just shy of 200 bucks.
Cost really depends on your setup.
You can get a bowl specifically made to house the tip of a heatgun, that plugs directly into your bong and be done w/ it. Water filtered vapo
You could fabricate a whip out of a chillum and home depot clear tubing. Buy a reducer tip for the heatgun and voila, you have a box/whip vaporizer.
with a top of the line gun, your setup probably would be somewhere in the range of 250-300 depending on what your preferences are.
If noise is an issue... paper thin walls or whatnot,
The 3g is completely silent, since theres no moving parts. I also think the learning curve is a bit easier w/ the 3g as opposed to a heatgun setup.