I'm working on a commercial game and I've gotten some people to play it, and as I expected the problem is the art(pixel), which I had to make myself.
Do you have any idea how I can get my game art made by a professional for free(or very cheaply), or maybe the best sites to get game assets.
Professional Art and Free don't mix. You get what you pay for; good art is expensive and takes many years of work to be at a level to produce.
If you want to get art cheap/free you'll have to offer something else, likely a share of game ownership. In that case, you'd better have a solid game from a gameplay prospective as a good artist probably has enough work to not need to risk joining a less than stellar project.
Hmm... Yeah, finding an artist partner would be one option. Need to offer him/her something in exchange though, which is not money.
Alternatively, buy ready made game assets from the dozens of marketplaces out there like GraphicRiver.net, etc. That is cheaper than paying an artist though.
Find a partner and share the profits. The art as you are finding is just as important as the rest of the game.
Quality tends to be mixed, but there are free resources:
https://opengameart.org/
https://www.gameart2d.com/
https://itch.io/game-assets/free