I've read numbers here in the range of $22k for replacing a 85 pack. I'm not sure what the warranty is on the new replacement packs that are apparently a modified 100 pack missing a couple of modules to make it a "90" (and also to keep it in the correct weight range).
If you're really driving to the moon every 3-4 years, I'd recommend getting an S with a 100 battery; I think some ravens and all "100D" have the lifetime 8 year warranty. I'd get the newest one of those you can afford
like this one. (it's a 2017 100 long range with 50200 miles so it only has the 2 year warranty, or for this OP, the 1 year warranty if he really pounds on 50k miles a year). It's less than a 3 or y at $58k
As far as if tesla ever will reduce the price of the replacement packs to the point where it makes sense to put one on a 500k mile tesla; the answer is total speculation. I personally put it at over 80% that they will make a somewhat modular replacement pack architecture out of the model 3/Y battery cells, and they'll price it at between $8 and $15k for a 90 size pack. Why? To burnish the brand -- they want to demonstrate that they'll be able to support the older cars forever otherwise they'll lose brand equity (buy a tesla? meh - they wear as well as an italian car!). Also, the whole premise of tesla is to scale up building a megacrapton of batteries and develop markets to consume those batteries; starting with the most profitable battery markets first (battery wrapping a luxury car) but eventually they want to be able to build terawatts of battery capacity and "replacement packs for older cars" will be more profitable than "packs to sit next to a house". If they want to dominate the EV market they'll need lots more repair capacity than what they have, and I'm guessing that 1/3rd of the bankrupted BMW dealerships will become tesla service centers by 2025. Lastly, the worn out batteries won't necessarily actually be dead, they'll just be really really slow to charge and have limited range -- having a bunch of those clogging up the supercharger network will ruin their thanksgiving surge capacity; it's worth while to incentivize repairing these older cars to avoid the clogged supercharger network and negative brand equity of "oh man that's an S -- I wonder if it's able to go 100 miles or not" like what you have with 2013 leafs.