River push in $300 live game

[Isaac Newton]

NL live cash $300 max table

Blinds $2-$5
SB $1,800
BB $400
UTG $600
UTG+1 $900
Hero MP2 $1,200
Button $1,500
all others are small stacks and not relevant

Action folds to Hero raises to $30 with AJh
Button calls
SB calls
BB folds

Flop AsAc5c

Checks around

Turn 9c

SB checks
Hero bets $100
Button folds
SB calls

River 5h

SB push
Hero: Did, did you say All-in????!!!!!!

This was a must move table and I had been there for about 10 hands. I played 2 hands and won both. One was a call on a river c/r from a known LAG to take a decent pot.
The villian had not played a hand since I had been there and I had never seen him before.

I took a while to play because I had no idea what to do and I still go back and forth on the right move here. Any input is appreciated.