Without knowing more specifics about what you are looking for it is hard to recommend something, but I have two that I really like for under $20 and both are a velvety plastic so that are an 8 on the material safety scale. For a traditional vibrator I have the Black Magic by Doc Johnson for $11.99 - I wrote a review on it and there are quite a few other reviews. The other one I have is a G-spot vibrator - it's the Dream Massager G by Cal Exotics for $18.99 (there is also a non-G-spot version of this for the same price). I prefer this one because the vibrations are stronger than the Black Magic. I haven't reviewed it yet, but if it interests you and you have any questions I will be happy to answer them.

The Velvet Touch by Doc Johnson is also a great choice for that price range.

Power wise I'd say the tattooed one by Doc Johnson, takes 2 C's, wicked power!

The Fun Factory Astrovibes are on sale now for under $20. They're pure silicone and rated 3 or 4 vrooms.

Although slightly more than $20, the "Lucid dream No. 14 – g-spot vibrator" is a really good feel for boys or girls. You could set an alert to watch for a price drop.

I got the iconic smoothie it is nice! It is quiet and has decent speed not high enough for me though.

I just got the Wanachi link This is really nice also. 8/10 safety I really recommend this one except it is loud! Like really loud, but it works great!

I know you said material safety over 5, this product says it is 2 but that is because there is a jelly sleeve on the bullet. I did not like the sleeve just the bullet it is awesome bullet though. The bullet itself is plastic. The sleeve is unnecessary. link