I am trying to avoid spending a bunch of money on a Mac Pro. My MBP came with 4 GB ram, 10 years ago. I recently heard somewhere it was possible to increase it to 6 MB. I talked with a tech at ifixit.com and found out it was in fact possible. Ordered the part on line (about $95 with shipping).
The part arrived two days early--yahh! The repair took less than 10 minutes. Most of that time was spent finding a small philips screwdriver. My MBP booted immediately. I am thrilled with how much better it is working.
Do not hesitate to resurrect you older machine. A year ago I replaced my MBP keyboard with a part from ifixit. I may never buy another computer.