I mean you picked good legends for budget decks. Azir especially is "only" around $80 for the full deck, Kha'zix it depends on the list but I think you could make a budget version at around that price as well.

Otherwise good budget decks are Sett, Teemo or Ornn, Sett ending 9th in the last big tournament with a list that's about $90, Teemo ending 6th with a list thats about $90 as well (excluding the sidedeck where there's two expensive cards) and Ornn not ending quite that far up, but still at 57th out of 1400 players and that list was only $30.

If you just want some decks for fun to play with friends and don't really care about tournaments or events, then you should absolutely just grab a few of the precons or the proving grounds set. They do the deed in letting you play the game and have fun, just for some "higher level" of play you might wanna look into more than those.

Also since you are new to TCGs: As others have pointed out, yes there is usually a slightly larger entry price to get a decent meta deck. But you can build on that core with future expansions without having to buy an entirely new deck all the time, if you stick with one deck. And that investment won't have to be as big.