I followed a different path many years ago when I converted an early-2011 MBP with a second internal drive, making the boot-up drive a then-spendy 120GB SSD (something my student loan helped cover), and
moving the /Users directory to the OEM HDD in a second slot (where the optical drive was). I still have the original Superdrive and the external USB case for those decreasingly frequent times I need to burn a thing. The really useful thing was I did have an HDD in there fail once, but the system didn’t freeze on me (the volume simply vanished as the system stayed up and running), and it afforded me a means to retrieve the fortnight’s worth of data which hasn’t been backed up elsewhere.
As with you, I don’t have much money to spend on gear. At all. Much of what I own are things which were given to me by folks who no longer had a use for them. And that gear which I do purchase is usually for long-term data conservation methods, such as RAID 1 redundancies for data I cannot lose (enter that FirmTek SeriTek 1V4 PCI card solution for my older-than-PCIe G5; the 1V4 was pretty inexpensive used and it’s afforded me a stable way to boot from SATA drives which were factory-rated at higher than SATA I/1.5Gbps speeds without having to look for jumpers).
As for this PowerBook G4 SSD conversion, the entire thing (250GB NGFF m.2 SSD + m.2-to-IDE adapter) amounted to ~USD$51, all-in, to basically boost overall responsiveness by 25%, much greater data reliability, and a reduction of heat and power consumption for basically the rest of its operating life. The near-flawless PB itself was a chance find at ~$63USD, and the CardBus dual-band wireless-N router was another USD$8. Basically, USD$125 for a modernized DLSD 17" in excellent shape is a lot of money for me, but I also know I’ll be using this setup for quite some time to come.