Tough river spot bet/fold or ch/c?

[SA125]

Full live 2-5

Limped family pot I have blk 4's in the CO.

Flop K52r ch'd around.

Turn 4 Good tag bets 40 from the SB. Folded to me I make it 100. Unk button coldcalls.

I have no read but others know him. I'm guessing he aint dumb but don't know if he's tricky. I'm thinking A3, 2P, or maybe a 3 in some crazy combo if he thinks I'm making a move. SB folds.

River J. We each have 500 behind. 300 pot. I'd hate getting raised, but I'd hate to pay off more than I would if I blocked a decent amount, say 100-150. What's the best line?

If you ch and he bet's 200, call or fold?