There is a 3000 KENPC limit for payout on a book in KU, not 300k words. Estimate 250 words per KENP. (Kindle Edition Normalized Page Count) So that's about 750k limit for getting paid for page reads on a single title. Just don't bundle your entire series together and you'll be fine.
As for physical books, I did have to go with a hardback version of an omnibus (279k), but I was able to print it through IngramSpark. I believe their page limit is 900 pages for paperback, and 1050 for hardback.
If you use Vellum, which I highly recommend, it really let's you play around with how much you can pack onto a page without it seeming cramped, with font choice, font size, spacing, chapter heading layout, etc. It's SO EASY and simple, and comes out looking fantastic. It's great for everything except math or non-standard text heavy non-fiction and LitRPG (because of the tables.) My upcoming paperback book release will have an average of 380 words per page, which is very reasonable and helps to keep print costs down.
However, I do think splitting the book (As long as the story allows it--you don't want to anger or disappoint readers!) will be your best bet. Rework your new ending and your new beginning to make sure things are impactful and satisfying (cliffhangers can be satisfying too, if done correctly) if necessary. One more book is an extra 33% possible revenue, and makes the series more appealing to new readers who want to binge it. An extra opportunity to advertise with the "candy" of the new release helping the Amazon algorithms, etc.
Edit: And to answer your original question, I think $3.99 to $4.99 to start, and then higher prices on later books. Personally, I'm $4.99 to $5.99, and am considering raising my average price by a dollar for testing. Remember, the price isn't set in stone. Some readers want a bargain to be willing to try you out, but there are actually a lot of readers out there that believe price signifies quality, and are MORE likely to buy a higher priced book.