1. The starting point is getting the visa fixed, if possible. Not sure why that wasn't attempted originally. OP says that it was "probably" caused by a policy change, but this suggests that OP doesn't know for certain. For $1,600, I would certainly be on the horn to the Consulate to determine whether this is fixable.

2. Presuming that it is not fixable, by the terms of OP's own email cut & paste of the fare rules, the change fee is $275 and there is an additional $25 TA fee. I have no idea what the fare difference is, but it's likely $500, leading to the $800 pp. cost.

3. I would not delay. The largest component of additional cost here is the change in air fare. That's likely to increase, not decrease over time as others purchase the cheaper seats. Thus, I would get this resolved sooner rather than later.

As an aside for others, it's important to get visa issues straightened out before purchasing non-changeable tickets.