Lots of B450 and B350's in the $100 range which will run 3rd gen Ryzens just fine with a bios flash. The MSI B450 A pro is a sweet spot as it's the same board as the Gaming plus without RGB and they both have the same VRM as the Tomahawk and can support up to an R9 3900 without an issue..Yeah, I'm going to wait. $370 is way too much for a motherboard, though. But I will check out AMD's offering when I go to buy. I didn't see a lot of reason to go AMD with the price of the motherboards currently.
R9 3900x plus the B450-A pro would total under $600. If you can find some 3200 mhz DDR4 cheap enough and reuse your power supply you could probably squeeze in a 2080 TI AND a brand new top of the line processor.
3700x is extremely close to 9900k performance at stock clocks for $325 so for sure, reusing some parts you could get it all squeezed in to the $1,500 budget. Which is crazy since the 2080 TI is over a grand on it's own