building a flow bench?

How expensive are those?

You can build a simple "manometer" at home. (manometer is a gauge to sense pressure drop).


Just get some clear plastic tube and put it in a u-shape. Partially fill it with a fluid (water will do), and then when a pressure drop is applied, the fluid on one side will raise higher than the other. You then measure the difference in height between the two fluid columns. The viscosity of the fluid will determine the sensitivity of your "gauge". It's crude, but it will work.

But if you want a plug-and-play system, that may be worth looking into.