NL50. Big pot. Three of a kind on river. How much to value bet?

[Haplo]

No info. on villain.

Full Tilt No-Limit Hold'em, $0.50 BB (9 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

MP1 ($10)
MP2 ($50)
Hero ($50)
CO ($32)
Button ($48.50)
SB ($47.25)
BB ($49.25)
UTG ($124.55)
UTG+1 ($36.50)

Preflop: Hero is MP3 with 2, 8.
[color=#666666]3 folds</font>, Hero checks, CO calls $0.50, Button calls $0.50, SB completes, BB checks.

Flop: ($2.50) 2, 3, 5 [color=#0000FF](6 players)</font>
SB checks, [color=#CC3333]BB bets $1.85</font>, [color=#CC3333]Hero raises to $5.5</font>, CO folds, Button folds, SB folds, BB calls $3.65.

Turn: ($13.50) 4 [color=#0000FF](3 players)</font>
[color=#CC3333]BB bets $6</font>, Hero calls $6.

River: ($25.50) 2 [color=#0000FF](3 players)</font>
BB checks, [color=#CC3333]

Hero ???? How much do you bet here?
Thanks.