I don't think you can get what you want at your price... yet.
The 4K monitors I have seen are deficient in some spec.
The Samsung UD590 perhaps comes closest, but is still more than your budget.
IN addition. it can do 60hz only by sending signals via two hdmi cables and matching them up on the screen.
If 30hz refresh rate is ok with you, there are 4k TV's that will do that at your budget.
But, they are not suitable for a gamer.
I am also considering 4k, and have a decent budget, but I do not yet see a 40" monitor.
I think smaller will make ordinary text too small.
SEIKI is supposed to launch the 40U4SEP PRO in a few months, I am hopeful that will be the one.
I might suggest that you look at a 30" 2560 x 1600 monitor for now.
I am pleased with the nixeus 30 vue and the yamakazi 301 Sparta.
You can orcer the yamakazi direct from Korea at a reasonable price.
/pcpartpicker.com/part/dell-monitor-p2815q
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