I looked recently for a "back up" cheapo as my current back up is running that software that MS will not support any more.
I didn't buy anything.
The "deals" from the net seemed to me to vary daily. I could not find a "right" answer. Ferkin dynamic pricing has a lot to answer for.
When I have to I think I'll give it an hour or so of net research and just go for the best deal available that day. I'll get it wrong, and find a better deal to-morrow, but such is life.
PS When looking for a pc for no 2 daughter last year, a "one-off" from PC world was cheaper than the internet cheapos. I guess they have to clear stock every now and then. She says it works fine. It was an Intel i5 whose number began with 3, after they had introduced all numbers beginning with 4. Stock clearances can be handy.....