Deck1: Karmov, Wonald, Varoslav, Pyro, Askai, Radek, Rodney, Mindy = around 9k
Deck2: Karmov, Wonald, Varoslav, Pyro, Holly, Cherry, Veronica, Brittany = around 6
Deck3: Askai, Buba, Boohma, Scopica, Radek, Rodney, Pegh, Mindy = around 14k
Deck4: Bankee, Annuqa, Ayzkub, Tsuka, Lena, Muze, Brittany, Lucy =around 13.5k
Deck5: Mawpin, Pan, Azel, Artus, Miss Stella, Jautya, Aleister, Murray =around 14.5k
Deck6: Neil, Dreen, Flanagan, Lolly, Jakson, Harvey, Flinch, Morgan =around 11k
Deck7: Any combination of this decks
You can change some cards, fe Wolgang in Freaks part, Tsuka will cost less in a week and so, but IMO, this decks are nicely balanced and are under 15k.
Hope it helped
Mono Jungo would be my best bet, many of their staples are cheap commons.
Roots are also very cheap, though they're not exactly newbie-friendly.
All stars have some excellent cheap cards for beginners, but sooner or later you'd want to save up for robb cr and marina.
Of course if you have no sense of shame, you can always go with mono rescue