The clear balloons from AliExpress are the most economical way to fly superpressure balloons. They cost in the range of $1.50 each and two are required. They have survived at least 9 complete circumnavigations of the earth. They float a little lower than the SBS-13 so they are a bit more likely to run into weather and fail. The most important issue is the quality control at the manufacturer is not quite good enough.
The balloons can be inflated with gas and used as is but you run the risk of having a defect in the plastic that you do not see. If that is the case, the balloon may begin to leak during ascent or it may develop a pinhole leak in a day or two. You can increase your probability of success by prestretching and endurance testing.
The balloons are able to tolerate about .5 psi differential pressure. If the balloons are inflated to .5 psi and held there for a couple days, the failures of the seams or the development of pinhole leaks will be detected and the good balloons found. It is not uncommon to lose 20% or more of the balloons but at that price it makes sense.
The equipment needed to do that is simple. An aquarium air pump, a pressure guage for HVAC types of work and a glass cylinder or jar able to hold water about 18 to 24 inches deep (to be used for pressure control). For removing the air, a second air pump of the type suggested can be modified to be a small vacuum pump and used to pull out the air.
The air pumps at about $10 at amazon can be found under the title Tetra Whisper Easy to Use Air Pump for Aquariums
Instructions on how to convert it to a vacuum pump are here: https://www.instructables.com/Reverse-aquarium-pump-to-vacuum-pump/
There are probably quite a few pumps that can do this and this is just what I found.
A pressure guage is also needed. I found this one for about $30 on eBay: Digital Manometer Differential Pressure Meter Gauge 2 Pipes Air Flow Test ±2.999
The air pump feeds into aquarium air line, a tee routes one line to the cylinder filled with water, the next tee connects the pressure guage and then the line continues to the balloons with one tee per balloon until the last one. When the air pump is plugged in and air begins to flow, pinch the line after the water cylinder line and adjust the depth of the line so the pressure guage shows the pressure you like and just let it run. When all the balloons are filled and stretched, the excess air will bubble out in the water. Just let it run and see which balloons fail. A failure will either be a pop or the bubbler will stop. If the bubbles stop, pinch off the line to one balloon at a time and watch to see if the pressure is increasing. That will find the failed one and it can be replaced.
When you are satisfied that the balloons will last, switch the air pump with the vacuum pump, pinch off or close the line to the water column and wait. The air will be gone in a while.
SF-HAB 