GTD :
You can run that system easy starting with any 550w certified 80+ bronze psu or higher on up wattage psu but look for a good gold or platinum certified psu seasonic corsair etc depending on your psu budget or noise level fans hybrid fan mode or whatever features you care for your future psu to have Wattage wise starting from 550w and you are fine can go higher like 650 or 750 if u want to sli/crossfire in the future.The tendency in new video cards its power eficiency just look at the new gtx 980-970 cards that need less and less juice to run so the era of monstrous psu is over
Sooo, if he will burn any parts based on low wattage, will you pay the price for them?
Based on the below link, it`s recommeded a MINIMUM of 550-600W for the R9 290x, without any OC on the GPU or PSU:
http://www.guru3d.com/articles_pages/radeon_r9_290x_crossfire_vs_sli_review_benchmarks,4.html
OP, don`t cheap out on the PSU. It`s the only component that can damage other components in your PC.