With that price it isn't a bargain because we don't know how old the rig is and if there's any warranty left on those components. To give you an example a 290x is a 4 year old card and 2-3 years ago a new one with a 3 year warranty would cost you over $500. One that's past its 3 year warranty and was mining for those 3 years may fail at any point and even if it doesn't it's still worth maybe $200, if you're willing to take the risk.


That rig probably won't make it long enough to give him any significant profit. It might be worth it if the  seller were to add all the boxes, so that you can mine fora couple months, dismantle it and sell cards individually as used. That might turn up some profit.