If you want some advice on potential substitutions, you can post a decklist here and we'll see what can be done. A lot of the shit cannot be substituted, like you can't have Dance of the Manse without at least 3xDance, 3xDoom, Magic Negro and the boardwipes.
And we're not even at the manabase. But that's true for almost every deck that aspires to be competitive. You need a pool of rares to work with.
When I started playing, I went over my collection and the starter decks and tried to determine if I had any useful rares. The popular choice back then was Mono U tempo, cause it was pretty much all uncommons and four rares (none of which were lands), one of which was in the starter deck. This approach may not steer you to the deck you want, but you need something that looks competitive enough to give you wins without too much pain.
Otherwise, you're back to grinding the play queue with starter decks.
Rares are the main bottleneck, unfortunately. You can make do without rare lands if you go monocolor, two color decks are doable, but good luck building a control deck without boardwipes, and most of those are rare, or the good 'wankers and win conditions.
Midrange also needs all those high-value rares and mythics, Aggro can be more forgiving because all you need here is to curve out reasonably well, and as long as it dishes out damage effectively, you might get results.
Though I agree, you'll need pretty much everything at the beginning. A lot of the uncommons are the meat and bone staples that can be good enough to throw together a budget brew. Even the simple Cat in the Oven needs eight.
Standard Event is a good source of those, but you'll still need a decent deck over there - should at least be capable of getting three wins. Otherwise you're just throwing gold at the uncommon casino.
The environment might be a tad friendlier than Gold Ranked, depends on the time of the day. You should expect mostly aggro, but I would make two variants of the good deck I had - one good vs. aggro, another good vs. control,
and swap them out if it felt today was the Chinese botnet was having a RDW Tuesday.
If your goal is to get specific cards, fastest way is note which cards you need, sort them by expansion. Check which expansion has the most cards that you need and buy packs from that expansion.
10 000 shekels should get you around two rare wildcards (sometimes they pop randomly), and if you get lucky, maybe also a rare that's on your wanted list straight from the packs.
You can definitely count on getting specific uncommons this way.
This gives you your baseline rate of acquiring rares that you need. The faster you can get a 10 000, the better for you. The game's a grind when you're F2P, but it gets easier as your collecton grows.
I like to set the goal at 10 000, cause it gives you a decent chunk of cards and you will genuinely feel the progress. It's also the price for two draft entries, and as I said earlier, it's a nice goal to be working towards.
It's a grind, but that's life as F2P. You can try and fork cash, but I reckon you'd be disappointed if you just buy packs with gems. For best pay-off, you'd have to draft... which means your nose goes down to the grindstone
in one way or another.
Don't be too hell bent on just one deck. For one, that deck might just prove to suck. Also, you might accidentally get cards to build a working version of another one, and that's cool as well. Even if it's just a BW lifegain thing with white pride mates, aerialists and the cat in the oven combo,
you might grow to like it as a change of pace. A good approach is to note which deck appers the most often, and gear your budget builds to pick it apart is as well as possible. As for now, the flavor of the week seems to be Feld of the Dead,
so you can pick a deck which can maindeck 4x Flame Sweeps (an uncommon craft) and Demolish and have a fighting chance against a decent part of the field.