under 200..?
well..that's actually too much for athlon2 x4 645..
this one is more than enough for your processor..Asus M5A97 R2.0 =>
http://pcpartpicker.com/part/asus-motherboard-m5a97r20
for just $90, you have $110 left for your graphic card..
for that price you can get gigabyte r7 260x=>http://pcpartpicker.com/part/gigabyte-video-card-gvr726xoc2gdrev2
so, for $200, you'll get mobo graphic card combo....
but if you insist to get a motherboard within $200 range, well, i recommend this one, Asus sabertooh 990FX r.2 =>
http://pcpartpicker.com/part/asus-motherboard-sabertooth990fxr20
One of the best am3+ mobo..