River value bet in BB vs BTN

[Spurious]

Poker Stars, $0.10/$0.25 NL Hold'em Cash Game, 6 Players
LeggoPoker.com - Hand History Converter

Hero (BB): $25.20
UTG: $8.60
MP: $49.95
CO: $37.75
BTN: $40.45
SB: $20.10

Pre-Flop: J[img]/images/graemlins/club.gif[/img] K[img]/images/graemlins/heart.gif[/img] dealt to Hero (BB)
3 folds, <font color="red">BTN raises to $1</font>, SB folds, Hero calls $0.75

Flop: ($2.10) T[img]/images/graemlins/diamond.gif[/img] K[img]/images/graemlins/spade.gif[/img] 8[img]/images/graemlins/club.gif[/img] (2 Players)
Hero checks, <font color="red">BTN bets $1.50</font>, Hero calls $1.50

Turn: ($5.10) Q[img]/images/graemlins/heart.gif[/img] (2 Players)
Hero checks, BTN checks

River: ($5.10) 2[img]/images/graemlins/diamond.gif[/img] (2 Players)
<font color="red">Hero bets...?</font>


Villain was 34/24/2

how much do we bet on the river?
I know he could have nothing, but in case he has something, how much do we bet?