You can't buy a new legitimate copy, but you used to be able to sell and transfer the license to another person. If you do not go through the process of transferring the license directly through Adobe then you have an illegal copy.
There is another problem. You are not going to be able to use a newer computer and OS for very long. The very next system update could kill your Adobe apps.
If you are just doing VFX and Graphics as a hobby then, like any other hobby, you have to pay what it costs to do it. If you are making money with AE and you still can't afford to subscribe then you are going to be out of business very soon. If you are a student you can pay for the entire CC suite by skipping one trip to the coffee shop per week. Any High School or College, or any legit school ID will get you a license for everything for next to nothing.