Some quick notes:
Avoid SanDisk SSDs for now. They had a terrible failure issue and do not really support their products since Western Digital purchased them. I posted links in a previous discussion if you want more info.
Samsung T5 and T7 are good SSDs. Just check the model (T5, T7, T9), color and size options to see what price is best. You can use CamelCamelCamel to check if “sale” prices are really a sale price. Strangely enough, certain T5/T7 colors will drop in price while other colors stay high. It is very random.
If you are not in a rush, use the Camel tracker to set price drop alerts. For example, the T7 2TB was recently around $165-170 for a while before jumping up to $200. If you set Camel to alert you when the price drops to $180 (or less) you can keep tabs on it. Prices will come down periodically, especially around Nov-Dec.
(Tip for searching on Camel: copy just the 10-character “B” code from Amazon’s product URL. So for the T7 I linked above, you only need “B0874YJP92” to find it on Camel. Amazon search also uses these codes.)
Additionally, while some SSD makes and models may be “slower”, keep in mind the faster speeds only really kick in when transferring large files. When backing up a lot of small files, things slow down just like if you got exit the highway and take residential streets with stop signs at every intersection. 
Every file copied requires the storage device (HD or SSD) to open a new file, write data, and then close the file. The open/close actions slow things down a bit. Super fast models are more useful when working with large photos or videos, for example.