There are exceptions to the rule that you always "get what you pay for". Indeed, there's nothing better than getting a good deal on a quality product. As the prices on flash drives drop, opportunities to snag a bargain are everywhere, but just because a drive is marked as "USB 3.0" doesn't mean it'll perform any better than an older 2.0 device.
The USB 3.0 standard has a maximum transfer speed of 640MB/s, excessively speedier than its progenitor, USB 2.0, which can muster a theoretical 60MB/s. Of course, due to operating system, micro-controller and driver overhead, you'll be lucky to attain anywhere near this sort of performance on a thumb drive.
There's also the matter of the flash chips used in the drive itself, with some providing better read and write speeds than others. Even drives from the same manufacturer can vary wildly.
Take for instance, SanDisk's "Ultra" series of USB 3.0 gadgets that have been on sale in various places recently, compared to the slightly more expensive "Ultra Fit" models. There's a noticeable difference in their maximum speeds, but it's the minimums that tell the real story:
Benchmarks sourced from USB UserBenchmark
Yes, you can get a 16GB Ultra for $10 right now, but an Ultra Fit is only a couple of bucks more expensive.
So next time you see a cheap deal on a USB 3.0 drive, hit up USB UserBenchmark first. It used to be the case that having a slow USB thumb drive wasn't a big deal (hey, I have gigs of storage in my pocket, woohoo!), but with high quality media hitting 1GB or more, the last thing you want to do is wait around while you "quickly" copy a few files to take with you, only to have "quickly" replaced with "slower than molasses".