This is pretty much THE BEST power supply under $40. It's better than the CX 430 and has more wattage as well. It's a tier 2 power supply on the EggXpert PSU Tier list (from newegg experts or something like that, can't remember) They don't get much cheaper, and using any PSU under $30 is taking a risk with your entire system.
I'd recommend this, it'll be perfectly fine for your needs. It can even support up to a GTX 650ti/7770 Ghz Ed. along with your FX-4100.