i would be beyond stunned if you could option a Model 3 to $100k, as that would logically bypass the entire point of the car and go against the master plan (step 3, "Use that money to create an affordable, high volume car." Unless you are very well off, $70-100k is nowhere near affordable).
I do not think that the options cost will be comparable to what we see on the Model S/X and should be much lower. The economies of scale that Tesla is working with will be very different and their deals with suppliers will no doubt result in substantial price reductions. If Tesla had to pay $XX for something because they only needed 10,000, the cost of that same part at the scale of 100,000 or more will simply have to be much lower. Heck even in my tiny little side business if I increase production from 500 units to 1000 it can sometimes cut the per-unit cost in half.
Elon said at the start that the selling price with "average options" would be around $42k. Taking $35k as the known low end, that would not seem to indicate something like $80-100k as the top end, but perhaps $50-60k. We'll see, and maybe I'm wrong but having another model in the Tesla lineup that options up to near 6-figures seems like a really stupid move.