As someone who used to play competitively a lot, and am just now getting back into it, I feel like it's important for beginners not to try too hard to be meta or competitive and to keep it fun and simple at first, while still trying to be as competitive as possible. This helps them to not be overwhelmed by all the little nuances of the game.
That's why I made glorious Gravekeepers <3
Monsters: [17] x3 Gravekeeper Spy (~$.50 ea) x3 Gravekeeper Commandant (~$1 ea) x3 Gravekeeper Descendant (~$.50 ea) x3 Gravekeeper Recruiter (~$5 ea) x2 Gravekeeper Guard (~$.30 ea) x2 Gravekeeper Nobleman (~$2.50 ea) x1 Masked Chameleon (~$2 ea) [Optional]
Total Price: ~$27.60
Super cheap monsters, except for Recruiter. If a beginner doesn't want to dish out 15$ for three recruiters, they can replace one with a guard or a Nobleman. Masked Chameleon is there for beginners who really want to try out/get the hang of Synchro monsters.
Spells: [11] x3 Mystical Space Typhoon (~$1 ea) x3 Necrovalley (~$.40 ea) x2 Book of Taiyou (~$.40 ea) x1 Book of Moon (~$.40 ea) x1 Dark Hole (~$.50 ea) [Should be replaced with Raigeki, eventually) x1 Royal Tribute (~$.50 ea)
Total Price: ~$6.40
Again, very cheap cards. The books let you abuse flips, which is fun. Also, there's no Upstart Goblins because they're relatively expensive and in a deck as slow as Gravekeepers, the extra LP actually has a noticeable effect. Necrovalley and Royal Tribute are the most essential.
Traps [12] x3 Imperial Tombs of Necrovalley (~$2 ea) x2 Mirror Force (~$3.50 ea) x2 Dimensional Prisons (~$2.50 ea) x2 Fiendish Chain (~$6 ea) x1 Bottomless Trap Hole (~$1 ea) x1 Solemn Warning (~$2.50 ea) x1 Vanity's Emptiness (~2.50 ea)
Total Price ~$36
As you can see, the traps are by far the most expensive part of the main deck. On the bright side, most of these cards can fit into a lot of other decks, meaning you can get a lot more use out of them. If a beginner doesn't want to drop the 6$ on Fiendish Chain, I'm not really sure what to recommend, but if they look around I'm sure they could find something.
Total Price of Main Deck ~$67
Extra Deck: [15] x1 Abyss Dweller (~$2 ea) x2 Wind-Up Zenmaines (~$1 ea) x1 Number 50: Blackship of Corn (~$3.50 ea) x2 Wind up Zenmaister (~$.70 ea) x1 Number 104: Masquerade (~1.30 ea) x1 Tri-Edge Levia (~$.70 ea) x1 Leviair, The Sea Dragon (~$3.50 ea) x1 Steelswarm Roach (~$2 ea) x1 Number 30: Acid Golem of Destruction (~$.70) x1 Black Rose Dragon (~$2 ea) x1 Stardust Dragon (~$2 ea) x1 Scrap Dragon (~$2 ea) x1 Black Rose Moonlight Dragon (~$9.00 ea)
Total Price: ~$35.40
This is about the best I can do with cards under 10$ (And I tried my best to keep them under 5, honestly). Extra decks are usually really expensive.
Total Deck Price: ~$102.30
With the deck, I tried especially hard to include the different mechanics. It has a lot of bounce effects, flip effects, control, the potential for synchro, xyz, special summoning, etc.
So yeah, keep in mind I'm kind of a beginner too, so everything I say should really be taken with a grain of salt.