How long have you been playing for? I suspect quite some time, so you've had the chance to build up a collection and target what you want. Rank 8 is not impossible, but very unlikely for someone that's just started playing.
yeah, quite some time, (I've almost F2P'd my way through all the adventures) but really if you can get a thousand or so dust you can put together a solid budget list pretty easily. just, like, do some research first so you know you're spending it wisely. you can usually get to around rank 15 or so with just basic cards if you're a good player, which gets you some good rewards.
always dust golden commons, the economics are strictly worthwhile. you get 50 dust for it, and to recraft a regular common only costs 40 so even if you want the exact same card, you net 10 dust by downshifting. this isn't true of higher rarities: they give you the same amount that it costs to craft a non-gold one, so only dust them if you don't want the card. but early on, don't be concerned about dusting them either if you don't need them, a golden epic can make you 10 regular commons, and that's usually a lot more valuable.
when you're starting out, aggro decks are a lot cheaper. most of their best cards are commons, whereas control decks often rely on legendary haymakers to close out the game. if you really want control, there are some options for budget finishers, but they're just not going to be as good, whereas in my current zoolock deck, for instance, I wouldn't replace
argent horserider with any legendary out there. it's just better. there's a couple legends that'd make my deck better, and I do run a couple epics, but the bulk of my victories come from hard-working commons.