Cable is expensive because it is stainless steel and most of the components are imported. I hope you aren’t using 2/4 posts.

Agree with Hallett & Co. 2x4 posts wouldn't be sufficient for use in deck construction. Would think 4x4 would be minimum but 6x6 preferred.

BTW cable railing in some places does not pass code. Can we see your house and I agree 2x4 not going to work. I actually prefer metal and glass railings I find the cables affect the view when seated. But I need to see your house.

Cable railing is usually sold as a system and it comes with posts. Like others mentioned I wouldn't use a 2x4 post for guard rails.

Here is an example of cable railing