You can replace that motherboard with this MSIhttp://www.newegg.com/Product/Product.aspx?Item=N82E16813130653
Save around $50
Change from the Asus version of the 7850 to the Gigabyte version.
Save another $20 to $30
you could get the locked version of the 3570, if you know they aren't likely to be overclocked. If you want to take the extra money saved by switching the MB and GPU, then you can get a decent aftermarket cooler and still save some with the unlocked core.
For a modular PSU, your gonna pay more than for an average one, but heres a decent 650w modular for a good price
Rosewill HIVE Series HIVE-650 650Whttp://www.newegg.com/Product/Product.aspx?Item=N82E16817182132
650w is plenty of power, it's what runs my system(I7-2600,16Gigs RAM, GTX 670)