AIO's are not always the best option. While they are more pleasing to the eyes, they are more expensive, louder, and dont last as long as a big air cooler.
For the the $40 dollar range, I would look at the Cryorig H5. You can always get RGB fans for it. If you have a little bit more money, then the Cryorig R1 is a higend air cooler. The Noctua NH-D14 is widely considered one of the best air coolers on the market, I just cant stand the way it looks. Another high end option is the Be Quiet Dark Rock Pro 4.
If you do go for an AIO, dont get a 120mm rad, they just dont cool well enough compared to a 240mm.