This cost varies based on the type of gas that you chose, as well. Purpose-built hydrogen (and some options for helium) regulators are very expensive, depending on the number of regulation stages and the regulation method employed. Simple balloon inflation regulators as shown can be easily modified for use with high-altitude balloons, are inexpensive to obtain, and can also be adapted to work with hydrogen. Note that there may be some issues with using helium regulators for hydrogen depending on your organization's level of concern over the use of hydrogen. Edge uses a high-pressure line connected to a balloon inflation regulator (in place of the push valve inflation nipple) and a hydrogen adapter (McMaster-Carr part number 7923A25).  Also, look at McMaster-Carr for professional-grade regulators.