Well , you could get a cheap laptop if you're not looking into doing any serious pc gaming.
If you really really want a desktop PC perhaps something like this would work, yes I very much like corsair ;), also I just picked any case but you should choose one that you like most, I think it's hard to fit a GPU under 400 bucks, maybe someone with more knowledge can.
But you can safely use the i3's integrated graphics (I would assume it plays hearthstone just fine) until you can afford a GTX 960 or something.
Silver player coins? you mean credits or platinum? unless you have some platinum you will not be able to trade at all, it's all about the plat.
Not sure about this frame specifically, but I've seen some full prime set blue prints being sold for like 50 - 100 platinum.
Also keep in mind that what people usually trade are blueprints and not the finished thing as far as I can tell(maybe they do at a higher plat price), so even though you'll save yourself some MASSIVE grind time you'll still need the shit load of resources those things usually require to craft, so you may still have a hefty portion of grind to do either way.