I'm a self-teaching violinist. I bought my violin 3 years ago and have been practicing since than. I'm a highschool student, so I don't have much time to practice, so I'm slow at learning it. (I'm practicing classical music, BTW.) Because of quarantine, I'm staying at home, so now I have much more time practice my violin, and I think I'm a bit better than before. Recently, I've had a feeling that I should change some accessories for my violin like the bow, string, and bridge. I wonder if it is worth buying something good for my violin, like a Pirastro Tonica (~$30), a bow around $40, and/or a violin bridge like "Aubert à Mirecourt No.7". My violin is a Chinese violin "Christina V02" that I bought for $98. I've been using the cheap accessories that came with it. I think the strings are around $5, the bow is <$10 and the bridge is <$1. What do you think? As a high school student, I'm low on budget, so I don't think I'd buy a new violin soon enough.
I'm a self-teaching violinist.
That's really the crux of the problem. If you had a teacher they would be able to give you far and away the best advice. I'm guessing you don't play in the school orchestra else the leader's advice would also be very useful.
Generally speaking the two things most worth upgrading in your situation are the bow and the strings. They are what, in the first instance, actually make the sound.
Tonicas would be a great choice for strings, particularly if you are currently using $5 strings.
For the bow I would try and get a halfway decent carbon fibre bow, but be prepared to go up to $100. At this low price point you will get a much better carbon fibre bow for your money than wooden bow.
It's almost impossible to give advice about a bridge over the internet, but the likelihood is that if what you have is a VSO (violin shaped object) then the cost of fixing the things that are wrong with it probably exceeds what it would cost to buy a decent student violin. Such changes would in any case have to be performed by an experienced luthier and that would cost. You can't just go out and buy a bridge over the internet and then make the adjustments (possibly involving cutting and trimming the bridge), adjusting the soundpost, etc., to improve the sound.
"I wonder if it is worth buying something good for my violin"
You are not buying it for your violin, you are buying it for you. The real question I think is whether the money will be wasted. In my opinion NO. If you are serious about playing and stick with it then some day you will buy a better violin and those accessories that are no perishable (like strings and rosin) will be put to good use.
As for the bow, $40 does not sound high end to me. Bows can cost 100's or 1000's of dollars for a good one and having played violin and classical bass my teachers always stressed the importance of a good bow. Some pros pay more for their bow than for the instrument. In many cases a low quality instrument will sound better with good accessories so it is worth it to try. Again, even if it does not improve you have better stuff when you get a better violin.