See
this post.
I believe your "seal elements per hour" number of 12 is a bit high, assuming Kagome is making seals near the limit of his seal-crafting ability. Hazou can probably achieve those numbers but non-Kurosawa have to be a lot more careful and spend a lot more time on seal verification. 6-8 elements per hour is probably more realistic, unless Kagome has some sort of sealcrafting acceleration stunt - which could well be the case, since his character is defined in part by throwing around excessive numbers of seals.
As they are likely to have the highest # of Sealmasters as well as the most intelligent ancestors (investors of their hereditary wealth), it's quite possible they're the second richest or even richest clan in Leaf. Speaking of which, we can now calculate the rough value of Keiko's bride price (assuming
Jiraiya & Shikaku both got a reasonably fair deal):
1) Losing Keiko will deduct roughly R910,000 from the clan's benefits per year
2) Gaining Keiko will add roughly 5 times that sum (~R5 million) to the Nara per year (As she's pulling from the 70% pool instead of the 30%, and the founding clan headcount is also low due to Senju, Uchiha only contributing 1 active duty ninja each)
Net Present Value of 1) + 2) @ an annual discount rate of 9% and assuming an ~average survival curve of 12 years would be R42.8 million according to this
NPV calculator.
3) Keiko's value as the Pangolin Summoner + Pangolin scroll added to clan assets
4) Keiko's value as a Mori Bloodline holder
5) Estimated economic value of Keiko's contributions not related to 3) or 4)
These are a lot harder to calculate, 3) especially as it includes the value of Pangolin combatants (multiple jounin at high levels), Pangolin trade and Pangolin techniques (acquired through trade or missions). I'm going to tentatively say it's roughly at the economic value of four clanless jounin plus the value of the pangolin gold contract that existed at the time the marriage was arranged, but with a hefty discount rate to account for the capriciousness and situational-ness of Summoning Contracts. The value of the techniques is immense but is handwaved into the relatively generous Pangolin trade calculation.
Net Present Value of 4 Clanless Jounin (R910,000 * 4) + Pangolin Trade (Moderately larger than the mortgage, we'll say ~R10 million / year) @ an annual discount rate of 20% and assuming a more conservative survival curve of 8 years = R52.3 million
Assuming 4 + 5 combined is worth about half of that, the total bride price would be in the vicinity of
R121 million, though all of this is in the form of hours, favors, and other non-monetary (or perhaps just non-liquid? They may have given lands, properties, stakes in companies etc) benefits.
Alternatively (and I think this is more likely), Shikaku may have paid 50% of the NPV in favors and hours to be owed immediately and the other 50% to be paid out over time (but without discount rates, and adjusting for inflation) every year that Keiko remains a member of the Nara in good standing.
Hazou's hand in marriage is also quite valuable, as any founding clan that acquires him would also benefit from 1) + 2), plus his potential income as a Sealmaster and his ability to make Sharingan babies. Assuming a 50% chance he makes Chunin and a 20% chance he makes Jounin Sealmaster, Hazou's marriage NPV is even higher than Keiko's. Kagome's hand might be even more valuable still, since he is already a Chunin Sealmaster and gets royalties from the Skywalker production of other Sealmasters.