river valuebet? how much?

[Guruman]

I've been active and aggressive at the table, and it's been flucutuating from 3 to 6 handed. I didt have any notes or stats on villain at the time.

Poker Stars
No Limit Holdem Ring game
Blinds: $0.10/$0.25
6 players
Converter

Stack sizes:
UTG: $25.15
UTG+1: $6.80
Guruman: $59.70
Button: $8.05
SB: $24.75
BB: $26.75

Pre-flop: (6 players) Guruman is CO with K[img]/images/graemlins/club.gif[/img] A[img]/images/graemlins/diamond.gif[/img]
2 folds, <font color="#cc0000">Guruman raises to $0.75</font>, 2 folds, BB calls.

Flop: K[img]/images/graemlins/diamond.gif[/img] 2[img]/images/graemlins/spade.gif[/img] 9[img]/images/graemlins/club.gif[/img] ($1.6, 2 players)
BB checks, <font color="#cc0000">Guruman bets $1.25</font>, BB calls.

Turn: A[img]/images/graemlins/heart.gif[/img] ($4.1, 2 players)
BB checks, <font color="#cc0000">Guruman bets $3</font>, BB calls.

River: 6[img]/images/graemlins/heart.gif[/img] ($10.1, 2 players)
BB checks, <font color="#cc0000">Guruman bets ...</font>

villain's line though passive is super strong given my bets and the board that he's facing. I'm basically hoping for a worse two pair here when I bet, and getting raised would be ugly, but I feel like I'm passing on too much value if I just check - especially given how aggro i've been.

so, i bet. how much?