Chris, I got it used off eBay for cheap like $40
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1311.R1.TR9.TRC2.A0.H0.Xmag nehelic.TRS0&_nkw=magnehelic+gauge&_sacat=0
You want one that can go to 1" I think so its not overly sensitive...
BTW the readings are all relative, not absolute values...