how about if we just inflate a balloon and connect that. you can rig up a few together for more volume. If you want you can fill it with smoke or from a vape pen. It wont apply a LOT of pressure and you can watch to see if it deflates and how fast or where the smoke is coming out. That's probably as easy to use as a gauge, and fits the budget.
If you want to get fancy there are vaporizers that fill bags of smoke. ( usually used for smoking"herbs")
https://ca.planetofthevapes.com/products/volcano-vaporizer
it has a little air pump inside, but you dont really need all that.
I think you can construct something more simple and cheap from a vape pen and maybe just use a hand pump or your Porsche tire filler device or use your lungs to blow in to supply air pressure to fill the balloon with smoke via a hose through the two ends of the vape pen into a balloon.