I have been looking at this one, for example. It's a USA seller, although the product is made in China. It's about the best seller feedback I can find with that model. It's affordable, has an 8mm transducer and does all types of metal. Read the description.
UM6500 Handheld Digital Ultrasonic Thickness Gauge Ultrasonic Tester Meter USA | eBay
Sellers with decent feedback are the ones with a better chance of taking care of problems like defective items and whatnot. I generally don't buy from a seller whose feedback is below 99%.