how much to bluff here

[knifeandfork]

.25/.50 live nlhe 7 handed
villain has ~70.00 i have ~100.00 utg straddles $1. villain is utg +1 calls he is a tad loose and a tad aggressive. utg is loose likes to chase but can fold and switches form aggessive to passive depending ( i guess) on how much he is stuck/up.
after utg +1 calls folded to me on the button i raise to $4 with AKo blinds fold straddler folds and utg+1 calls
flop is
QJ4r
villain bets 2.00 which means from him a weak draw or second pair about 90% of the time. i decide to raise hoping to take the pot later so i bump to 5.00 he calls.
turn is 7 putting a second heart up he checks, i bet 6.00. he says how much are you milking me for? and calls now if i wasnt sure before im 95% sure he has a jack with a decent kicker J9-AJ. river is an offsuit 9 how much do i bet here to induce a fold? i dont trust my read enough to push (or over bet the pot) and betting the pot in this game would be perceived as a "huge" bet? thanks in advance for your responses.
jason