OK, I commute with my bike every day and I kinda would like to know how far I'm going and more importantly how fast. I don't need anything difficult cause I'm just curious about stuff like that for fun.

I ride a Kona Smoke 2-9. Any suggestions on what kind of device I should get? I don't want to spend a lot because I'm a poor student so I would like to get something like $20 and below.

I picked up the Planet Bike 8.0 from Amazon for $19. If you're just looking for speed and distance (with fewer features such as max/average speed, trip distance and odometer, etc.) the Planet Bike 5.0 can be had for about $15.

I can appreciate the poor college student budget - that's where I am and I sprung for the 8.0 just because I liked the added features.

You can get distance online with several sites.

One is:
https://www.gmap-pedometer.com/

Divide that by your travel time and you have average speed.
All for free.

This one is currently on sale at Performance. You can usually find a cheap-o on sale at most LBS. You could also try Target/K-Mart big box type stores. They probably have a real inexpensive speedometer that will do what you want.

walmart...learn to love it as a college student...i do

Walmart $9.56 I bought two of them.
https://www.amazon.com/Schwinn-SW654-.../dp/B000DZD3FQ