A precision level I made in 2003. It is based on Swiss / German levels. The 3D Adobe Acrobat Reader (version 8 or higher) file (picture) allows rotating to see all sides. Level vial is glued or held with rubber bands to vial holder. Vial is adjustable side to side (Azimuth) and up and down (Elevation Inclination).
...... I bought level vial from http://www.wamoyer.com/index.html
The small cross level is easy to remove from any cheap plastic level. I milled base with a "flycutter" all at once with a wide cutter. This way V and flat base is aligned. Also milling extra in center 1/2 allows level firmly sitting on it's ends if concerned about base flatness not that I have seen any rocking on a granite surface plate. It is lower profile and more open than a "box" level and had room for a small LED light. It has an adjustment knob pushing against an o-ring spring. Design worked very good for many years.
..... Other design modifications are possible. I am just saying if you want an American made Precision Level for under $40 maybe you just got to make one yourself.