This is simply not true. Folks buy cookie-cutter and semi-custom boxes all the time and are perfectly happy with them. As for being the cheapest option, as with most things in life, it depends. Do you want tier 1 FRU's with capacity and legs, well surprise, it's going to cost you.
OP: The only way to get what's best for YOU is to bite your lip and spend some time learning for yourself.
NO it is true,because if you custom buld it you get best bang for buck if you know where to look for parts,but if you dont know then its all the same if you buy build up box.