Keep in mind that, as a DM Tool, it will be well worth the cost, especially if there it is just as a reference point, campaign mamager, character creator, and you have to include notes if you don't have access to anything more than the srd.  We also can't go by just what we see right now. ohase 2 and phase 3 are still to come. That is where my main interest is.

I am guessing there will be both subscription access plus pay once per book access, with the subscription unlocking everything as long as you are current and the pay once option only unlocking certain features, but permenantly.  With that being said, I hope that future physical books include a code to unlock access for DnD Beyond.  For previous releases, I think a range between 4.99 (for quest and addon books) to 9.99 (for core books) would be fair for new players as well as owners of the physical versions of these books.

$5-10 for a permanent book license is likely going to leave you very disappointed. I would expect that purchasing a book here would cost at least 3 times that, if not more. I arrive at my estimate using two methods: covering business expenses and incentivizing subscriptions.

Let's take a best-case scenario: they have one data entry person being paid an average salary, there are no other upkeep costs that the purchase is going for, and WotC is miraculously not taking any cut of the proceeds. On top of the wage, there are employment taxes and benefits, and from a quick search this leads to about a 25-40% overhead on base salary. The median salary for a data entry clerk in Huntsville, AL (idk the actual job title used by DDB) is around $29,000, add in 1.25x for the aforementioned overhead in the best case and that comes out to a bit over $36,000.

Now, at $5 per book purchase, assuming 100% of the proceeds went towards paying off the person inputting the data, 7200 licenses would need to be sold. This seems imminently reasonable. However, realize that the credit card processor takes a cut (around 2% for card not present transactions). WotC is going to want a cut as well, let's be conservative and estimate that at 30% (same cut for apple/google for their respective app stores, and since WotC is actually providing content rather than a service, I wouldn't be surprised if their cut was in actuality over 50%). Finally, the server infrastructure isn't free, and there's more than the one employee at DDB -- I count 10 DDB staff on the forums. Some of them have higher-paying jobs than $29k, so let's up the average salary a bit to around $50k + 1.25x overhead = $62.5k per person * 10 people = $625,000 for wage-related expenses. Estimate a lowball $10k/mo for the office lease plus utilities plus server/miscellaneous costs (times 12 = $120k/yr), and we get a grand total of $745k operating expenses per year, which we'll round to $750k to make the math nicer.

Now, at a 68% cut of the proceeds, that $5 turns into $3.40. This means in order to break even, about 220.5k licenses need to be sold at that price each year. The above numbers are all conservative estimates, in reality they will likely need to sell significantly more just to break even. 5e is popular, so 220.5k per year is within the realm of possibility, but it will take some time to get enough customers here to sustain that (only 87k members so far in beta, and not all of them are going to be willing to spend money here).

Finally, disregarding all of the above, the permanent book licenses need to contrast with the subscription pricing. DDB benefits far more from a continual subscription (guaranteed revenue stream) over one-off sales. As such, the pricing structure is likely going to favor purchasing a subscription as the "cheaper" method to get access to the content. WotC's release cadence looks to be about 3 hardbacks per year at the moment, and a sub of $5/mo will run $60/yr. At $20 per book, purchasing the books for a year is equal to subscribing for a year at a very low sub price, which isn't all that enticing as far as the sub is concerned. At $30 per book, you're better off picking up the sub if you want everything, since you are overall paying less per year than you would if you bought all the books individually, that is a good incentive to subscribe. And this is assuming a $5/mo sub. Increase the sub to $10/mo, and the break-even is $40 per book, and the more likely cost to incentivize subscriptions is going to be print MSRP ($50/book).

The above analysis has too many variables and unknowns to really determine what the final pricing is going to look like, but I would say that the lower bound on pricing is likely a $5/mo sub and $20 books.

I see your point, but keep in mind that there's more than one book being sold, at launch there will be twelve or thirteen.  You wouldn't pay that person to do one book, than sit back and wait on cashflow.  That person/those people will be doing multiple books, plus working on other aspects of the site.  Plus, perceived value needs to be considered.  How many sales would they get for a 20 dollar digital version vs. a 10 dollar one?  I would wager that many more people would purchase at 10, in the end making more profit at that price than a significantly lower amount of people purchasing at 20.  Subscriptions would hopefully only hover around the 5 dollar mark, or 60 bucks a year.  Much higher than that and many would rather just pay cash for the physical product just to have something tangible.  I know I will be using DnD Beyond as a supplement, not as my primary tool.  I'll still be buying the books as they come out to DM with, as there is a feel using the books that isn't there with a PDF.  That being said, having an online resource will be nice if there is a question that we don't want to thumb through page after page to find an answer to.