I need a power supply for $100 or lower that will work for a MSI A75MA-G55
>>378360
So any ATX powersupply basically, The motherboard it's plugged into doesn't really matter. You should be worried it whatever power supply you want will fit in your case and has enough power for your system.
Or if you have a standard case and just want an answer, search amazon for "600W atx PSU" and buy the first one with good reviews.
Just make sure it has the extra 4-pin 12V connector.