Rebecca's
$2.00
610 Bushwick Ave, Brooklyn, NY 11206, USA
Cheapest regularly-available beer found is a Rolling Rock bottle at $2, per a Bedford + Bowery profile of the bar (published Oct 2016): "cheap libations like $4 well shots, $6 mixed drinks, and beers as cheap as a bottle of Rolling Rock for $2." This is the only source with a specific price. It is nearly a decade old, so treat as directionally indicative of a cheap dive-bar price point rather than a confirmed current price.
Source: Bedford + Bowery
Marco's
$3.00
1071 Broadway, Brooklyn, NY 11221, USA
The cheapest regularly-listed beer is a Bud or Bud Light bottle at $3, per a Gothamist profile of the bar (published April 7, 2017) that itemized 'Regular Prices' including 'Beer and shot: $6', 'House and classic cocktails: $8', and 'Bud or Bud Light: $3'. That $6 figure is a beer+shot combo, not a standalone beer, so it is not the cheapest single beer. Because the only fully-verified price source is nine years old, treat the $3 figure as dated and re-check if possible.
Source: Gothamist
Post No Bills
$3.00
253 Bushwick Ave, Brooklyn, NY 11206, USA
Rolling Rock $3, Miller High Life $4, Budweiser $4 (bottles). Draft pints $6 (Pilsner Urquell, Founders IPA, Montauk). HH daily until 9pm: $3 Bud/MHL, $4 drafts.
Happy hour: Sun–Sat · 19:00–21:00 · $3.00
Source: postnobillsbk.com
Abe's Pagoda Bar
$4.00
108 Wyckoff Ave, Brooklyn, NY 11237, USA
Official menu lists Budweiser draft at $4 pint. No time-defined beer happy hour found.
Source: Abe's Pagoda Bar official menu
Bootleg Bar
$4.00
1438 Myrtle Ave, Brooklyn, NY 11237, USA
Dive bar with pool table and pinball. Mon-Fri happy hour runs 5-8pm with $4 drafts, plus an always-available $5 beer-and-shot combo.
Happy hour: Mon–Fri · 17:00–20:00 · $4.00
Source: Bootleg Bar Instagram