Finally finished again! I did a smidge better, but not by much...
Careers capped (2) = 2400
Lvl 6 = 200
Lvl 7 = 400
Total = 600
Rewards (29) 1.45=1.00=2.45
(2400 + 600) x 2.45 = 7350
Total: 7350
I am so glad to have this challenge finished. It was better this time, though. I can't wait to hear how some people maxed out 3+ careers.