First Commander Deck 101
Commander (1) ($-$10) 2 Colour 2-5 Mana <$10 Relevant but not crucial ability. https://scryfall.com/search?q=%28type%3Acreature+type%3Alegendary%29+cmc%3C6+legal%3Acommander+cmc%3E1+usd%3C10+c%3D2&order=cmc
Land (38) ($0) 38 Land 0-8 Duels (what you can find lying around) For the rest just use basic lands.
Removal (10) ($3) 4 Creature/Catch-All Removal 3 Other Removal 3 Board Wipes/Mass Removal Nothing over 20c for removal and 50c for Board Wipes or Mass Removal.
Ramp (12) ($2) 7 Under 2 Mana 5 Between 3 and 5 Mana The less mana the better and nothing over 30c.
Card Draw/Tutors or Recursion (16) ($3) 5 Recurring use 3 Cantrips 8 One card use
Staples (10) ($2) These are cheap commander staples in your colour under 20c each. Search under the commander sets for under 20c.
X Spells (2) (50c) These can do anything up to you. They should give a large advantage if you have X high enough.
7+ Mana Bombs (5) ($3) Nothing over 50c.
Other (5) ($0) Just other cards in your collection that you want to add.
---------------------------------------
Curve Land - 38 1 to 2 Mana - 22 Cards 3 to 4 Mana - 20 Cards 5 to 6 Mana - 14 Cards 7+ Mana - 6 Cards Make sure it fits roughly this ratio to 1 or 2 cards.
---------------------------------------
You should be able to win casually at power level 0-6 for roughly under $20 (If you have any base cards).
Good Luck!! ^_^