The average number of rolls is the inverse of the bonus-ending event, which has a probability of 1/6, so the player will roll six times on average. However, the last roll will be the seven, so an average of five winning rolls per bonus.
Next, here is the probability of each total, assuming no seven:
2 or 12: 1/30
3 or 11: 2/30
4 or 10: 3/30
5 or 9: 4/30
6 or 8: 5/30
So, the average win per roll, assuming no seven, is 2*[(1/30)*1000 + (2/30)*600 + (3/30)*400 + (4/30)*300 + (5/30)*200] = 373.33.
The value of the consolation prize is (1/6)*700 = 116.67.
Thus, the average bonus win is 116.67 + 5×373.33 = 1983.33.