I beleive the rebuild kit is called a cover set. The filter/screen is not included. It has been awhile, but I think I payed below $30 for my cover set and screen from Direct Line.
Correctly stated, that is what I paid. The other thing is, if your petcock is bad, it does not mean you will hydrolock. I won't go into detail, but if you understand how the petcock functions and is constructed, you will know a hydrolock is not eminent.