Pictured: aichose Brix Refractometer with ATC, Dual Scale – Specific Gravity & Brix, Hydrometer in Wine Making and Beer Brewing, Homebrew Kit – affiliate link, note that multiple variations of this product may be available, as such a different version may appear at this link
When I first started homebrewing years and years ago, refractometers were expensive. Homebrew shops were selling them for $50 to $70. Even now, it’s not economy to see off brand refractometers sell in this range.
Lab grade refractometers
Prior to regular use by hobbyists refractometers were generally lab equipment. along those lines a lab grade refractometer can cost hundreds or thousands of dollars.
What about $10 to $20 economy refractometers?
It’s not uncommon to see a dual scale refractometer for $20 or under. It’s my opinion that most of the economy, non lab grade refractometers are probably manufactured by a handful of makers. Or at the very least, the manufacturers are producing units of similar quality. You could easily pay $60 at one retailer and $20 for the same unit via another retailer.