Add evaluation costs to budgets

[jmsmkn]

With the increasing evaluation times challenge admins can now do quite complex evaluations that can use a ml.m5.2xlarge 8 CPU 32 GiB $0.461 / hour for 12 hours, giving an evaluation cost of $5 / submission. This can be significant so should be included in the challenge budget prediction, and also taken into consideration on the stats for cost / submission (pretty sure it already is, but double check).