Agree with the previous posts, however, the SP 18 on the D&S is likely to be a one time, short duration, event. So, you can wait for the D&S to run a public type charter with 100+ people trying to fit into some limited sites. Cost will likely be less than $200.
Or, take your chances and spend some money on one of the two quality charters being planned. The Trains one will likely have some snow on the ground, the Lerro trip will have a bit more sun time. Both are bad overall for sun except for the SB run portions. Later on is not likely to have much chance of many runbys due to other trains.
As far as the Big Boy, I too want to see that event. However it will be chaos at a lot of locations and likely a better chance for photos later than the May extravaganza. Any comments?