Calculate real TCO to put something DIY together that is comparable. Power, space, cooling, hardware, software, etc for something that is just as performant, fault tolerant (from the components all the way up to the datacenter), physically secure, firewalled, all managed for you, etc etc.
Chances are you don't think you need all of that and that is why you say you can do it cheaper. Most folks don't count their time or their employees either.
I'm not saying your wrong. I'm just saying folks that say DIY is cheaper are probably comparing apples to oranges.