A brebones system will still require you to drop another $200-300 on CPU, RAM, vid card etc etc. Can MAYBE put together an APU base system for $350 but youd be scraping the bottom of the barrel. Tell your friend to save his money towards a proper upgrade and not screw around replacing bits and pieces on a 8 year old PC.
More opinions about what? A barebones system is just that, barebones. It isnt complete, itll still need him to buy more hardware. And at you price point, it isnt going to happen. Thats why there hasnt been anymore responses.