If the only reason you're still using a mechanical hard drive for storage chores is capacity, not price, then Samsung's new 4TB 850 Evo solid state drive might be of interest. It's not the most capacious option out there—HDDs still offer greater amounts of bulk storage—but it is the biggest consumer SSD with plenty of room to hold large photo collections, videos, games, and so forth.
The new 4TB option doubles the capacity of Samsung's Evo SSD line, which previously topped out at 2TB. That additional storage adds up to a $1,500 price tag, however. At that price, you may have to decide between paying rent for the month or screwing over your landlord for a faster bulk storage option than that aging HDD provides. Use your own judgement on that one.
While expensive, the price works out to less than $0.38 per gigabyte, which is about par for course in SATA SSD territory. Still, it underscores the gap in pricing between SSDs and HDDs: A white label 4TB HDD can be had for around $90 on Newegg.
The 850 Evo is a much faster solution, of course, albeit it's bound by its SATA 6Gbps interface. Samsung rates sequential read and write performance at up to 540MB/s and 520MB/s, respectively, on the 4TB model. Those numbers aren't in the same neighborhood or even ZIP code as PCIe-based SSDs.
For those who can afford it, the 4TB 850 Evo is a compelling option for a single-drive setup, rather than buying a smaller capacity SSD for the OS and a larger HDD for that growing Steam library.