Villain is reggy (20/18/5.5 over 50 hands, average reggy agression factors postflop albeit small sample)

Given we're under-repped, do you want to call the river?

SB: $13.35 (133.5 bb)
Hero (BTN): $34.26 (342.6 bb)

Preflop: Hero is BTN with K A
3 folds, Hero raises to $0.30, SB raises to $1, BB folds, Hero calls $0.70

Flop: ($2.10) J 7 6 (2 players)
SB checks, Hero checks

Turn: ($2.10) A (2 players)
SB bets $1.42, Hero calls $1.42

River: ($4.94) 3 (2 players)
SB bets $4.24