I don't think this stat is already in the
Repository but you could build a Custom Statistic for it.
Have a look at the
Custom Stats FAQ for information on building custom stats.
To see the average amount bet you'll need to decide which bets you want to count (e.g. just the flop), and how you want to define the bet amount (absolute money amount, BB, or better the percentage of the pot), and sum up all of these bets and divide it by the number of times they made the bet.
e.g.
sum(holdem_hand_player_detail.val_f_bet_made_pct)
sum(if[holdem_hand_player_statistics.flg_f_bet, 1, 0])
