A few factors influence the price of an external storage device: how much storage you need, how fast it transfers files and its physical size.
External drives with high capacity and power adapters are now very affordable. This is a good option, especially if you don't mind carrying it around or don't feel the need to unplug it often.
There are a few options for those looking for something smaller and more portable, such as a USB-C drive with greater storage or thunderbolt SSD Drive for speed.
It can be very costly to find a drive that meets all these criteria. However, SSD prices are falling at a lower rate than expected so you can still get an external drive that has a lot of storage for a low price.
The transfer speed of an external hard drive depends on the storage type of your computer. A SATA drive may struggle to keep up with a faster external drive. Your rig will only be as fast as the slowest component, as is the case for most computing components.
A 2019 Razer Blade Stealth has a Thunderbolt 3 port. This should enable for extremely fast transfer speeds. However, the SATA storage in the Stealth had a significantly negative effect on the Thunderbolt 3 drive's maximum transfer speeds, in comparison to the flash-based storage found in the 2016 MacBook Pro.
Thunderbolt 3 SSD is the best choice if you want the fastest data transfer speeds and have the right ports and internal storage to support it.
This is twice the price of other options but twice as fast as the others. This can be a significant difference if you have large files.