I'm not sure that's the best of both worlds...there's a lot of hardware out there that is low quality or just doesn't work well with other things, and if you similar quality hardware you're probably not going to save much money.
Plus running MacOS on a home-built computer is not supported and even if you only get hardware that works with it you can easily waste a lot of time. Maybe it's worth the trouble if you're on a very tight budget, but if you can afford to just buy a Mac I think it's well worth it.
As for a cheap PC running windows...well...I think that's one of the best things about having a Mac - I don't have to deal with windows bullshit or half-assed garbage hardware that a lot of PC manufacturers (and even manufacturers of many off-the-shelf parts) sell anymore, and I don't give money to what I consider one of the worst companies in the history of computers.
...although if Apple continues with certain practices like soldering RAM into some models I'm going to be very disappointed in them too. That's why I don't recommend some models like the 21" iMac right now by the way.