I think the biggest one is the cables, I know my uncle spent about $3500 on cables for his home theater. And its a basic 5.2 setup...
I like bluejeans, Monoprice, audioresearch, ect for my RCA's, I recently bought a pair of Emotiva XLR's {because they were short} and a Emotiva toslink {also short} but all 3 cables were under $70 shipped for all 3 cables {and I still felt dirty}...
But for speaker cables, I make my own, just buy 12 ga copper wire {real 12ga} from amazon, if I feel like spending more Knukoncepts Karma cable is nice but costs almost double {$20 vs $40 for 50ft}, and pick a banana connector you like.. I use the sewell deadbolts they are $1.25 ea.. If you want to be "fancy" just for looks, you can add knu's wire pants, and some techflex...
25ft 12ga-$12
25ft 3/8" techflex-$7
24 bananas-$27
10-10ga wirepants- $15 {get the 10ga if you are going to use "real" 12 awg.
So for $60 you can make 5- 5' cables, thats less than $10 each, and ad another $20 you can make 5-10' cables....
And they do the same thing as the $20 per foot cables..