A quick Google search will yield many results. Amazon will also let you compare. Mine is not top end but great as is. No need to spend a fortune just get one that works for your budget but has decent reviews. Foot comfort is the main thing as you are hanging upside down suspended mainly by your feet/ankles.
If you have a health food store in your area ask them as they're likely to have some insights on where to buy. Yoga studios as well are good places to get advice on where to buy. Especially Iyengar Yoga as they do a lot of inversion poses and promote hanging upside down for longevity
Be well...
Wade