Coconut oil! It is natural and cheap. Make sure to clean, condition and brush it out before applying it. I’ve also heard that braiding it or keeping it in a tail bag helps!
There are tons of suplements. Idk how expensive they are. Biomane looks worth buying it.
Try by applying coconut oil on the mane and tale, this will really help strengthen and thicken the name and tail.
Mane and Tail works great! But there is also some other specialized products that help just as well. With some horses, we wash their mane and tail with Mane and Tail about once every two or two and a half weeks just to keep up with it.