The rule of thumb is 10 - 15% of total budget. But depends on your components. One thing I learned early on, with modest components, be careful of too transparent interconnects. My system didn't sound better with truly neutral interconnects until my components were at the $5K level. Before that slightly warm interconnects that would cover up some of the deficiencies in the components was helpful. My first jump into high end cables, Straight Wire... was a disaster. Highly reviewed cables, sounded terrible. Thirty years latter I pulled them out... they are simply fantastic... with the components I had then about $7K each... when you get to a certain level, you want transparency, but before that you want some protection.
Look at Cardas and Wire World, other brands made of copper... maybe silver coated copper. Stay away from all silver.