I bought these. https://www.amazon.com/dp/B00OQG7IC2/ref=cm_sw_r_cp_apa_fab_TROzFbQA242DA They are amazing. The noise isolation they provide is amazing and they are super cheap.

What sounds are you looking to avoid? These work best for loud machine sounds. They also work well at subtly telling your coworkers to stop chatting. If you can also try cheap ear plugs from the drug store.

Alternatively if you are trying to drown out chatty coworkers then you can use these headphones with some white noise playing through them. I also found that having a techno or low fi track on repeat worked well.