...While the price of more capable PCs is very low, the software is the issue--I have to buy Windows pro (for networking) and Office, and a bunch of other apps..... And then there is the cost of setting everything up....
You don't have to purchase Microsoft Windows or Microsoft Office. There are free alternatives. Instead of Microsoft Windows I run the Ubuntu distribution of GNU/Linux, which has very good networking, including Samba, which provides compatibility with Microsoft networking. Instead of Microsoft Office I use OpenOffice, which provides all the word processing and spreadsheet capabilities I need. Instead of using Adobe Photoshop, I manage with The Gimp.
Setup is still a cost, of course, but sometimes you can find someone willing to set it up for you, in exchange for some of your time.
I have been watching computers become obsolete for a long time. Almost always a computer is discarded because it doesn't have enough memory, so I advocate getting as much RAM as you can afford. When I got my current computer, several years ago, there was a problem with the motherboard. The shop that built it for me was willing to replace it at no cost, since it was within the warranty, but I asked them to replace it instead with a motherboard that would hold more RAM, and to install as much RAM as the motherboard would hold. As a result, my computer, though several years old, is capable of running modern software.
If I were buying a new computer today, I would get one with 16 or 32 GiB of RAM and a 64-bit processor. I would count on being able to add external hard drives in the future, but you can't add external RAM.