I bought a used Dell Inspiron 1545 two years ago for 40 dollars, and I recently upgraded it a lot. It is an old model, but I've been happy with it. For being over 10 years old, it performs fine.
Here are the current specs:
2TB ADATA SU800 SSD
8GB Kingston PC2-6400 DDR2 RAM
Intel T9600 2.8GHz CPU
BluRay RE Drive
Here are the before specs:
160GB HDD
3GB DDR2 RAM
Intel T4300 2.1GHz CPU
DVD-RW Drive