Does it really matter? Presumably the original designers didn't decide to base the stutterwarp drive on Ta-180m and then work out how many ships that would mean. Rather, they decided how many ships they wanted around and came up with the rubber physics to make it so. If it hadn't been one piece of handwavium it would have been another.
They choose Ta for the distribution pattern of reserves. Happy coincidence they picked the only element with a stable high spin nuclear isomer.
So if anyone wants to change the 2300 setting to one where rag-tag bands of adventurers can own their own ship, they'll have to change something in the underlying assumptions anyway. Whether that is to change the bottleneck isotope to something less rare or to make some other change, the actual real world rarity of Ta-180m becomes totally irrelevant.
Consider this old post of mine from etranger:
For a while I've been considering the worth of a starship.
A typical 25,000 m3 transport can (potentially) turn over MLv40 per year
(assuming 333 vly moved per year @ Lv5 per m3/vly, with the ship being serviced
twice a year for 2 weeks at crew change).
The costs will be:
Crew: MLv0.6
Fuel: MLv1.5
Power plant maintenance: MLv4.5
Other systems maintenance: MLv0.62
Life support: MLv2.16
Total: MLv9.38 (round to MLv10 to add various charges etc.)
The ship thus has a potential profit of MLv30 per year, and likely does over
MLv20.
At MLv30 profit per year if the ship were a unitary corporation and the price to
earnings ratio was around 10 (i.e. typical, not in a bubble or depression) then
the starship would have shares totalling MLv2-300 issued on them. Assuming only
100 shares were issued then they'd cost MLv2-3 each and pay a dividend of
MLv0.2-0.3 per year. The cost could easily be double that.
Now, lets have a look at the construction cost. For a ship of this type the
construction cost is ca. MLv6. The actual construction cost of a starship is
equal to only 1-2% of the value when floated. This would make constructing and
operating a transport starship probably the most profitable business ever.
Now, what drives prices up this high? The rarity of starships. If there was no
restrictions on building them then transport prices would tend towards cost only
with profits minimised to gain competitiveness.
As an analogy I may use the housing market. A typical British 3 bedroom house
costs a bit less than £50,000 to build at the moment, yet in London would trade
at over £500,000. At a tenfold return it's difficult to see why more houses
aren't built, but of course the issue is the availability of land. It is this
very lack of a vital resource that drives house prices up.
It's the same with starships. The lack of tantalum is likely the limiting
factor. NAM deals with cost, not value.
Now this brings me to my next point. Assuming the ship is divided into 100
shares, who owns them?
The original owner (almost certainly a government) takes the profit of MLv20-30
per year, but maybe needs a quick cash injection and so decides to sell off 10%
of the shares, and gets an immediate income of MLv30 or so, at a long term loss.
They can do this quite a lot and as long as they maintain a controlling interest
(51%) it's still "their ship". Thus you probably have situations where a ship if
60% (say) owned by (say) the French government, but the remaining 40% are
circulating shares and simply return a profit.
Now, this is of course risky. Might we not have investors instead of putting
large lumps of money in one ship preferring to spread out their investment
amongst many ships. Thus we have the idea of having a portfolio of starships in
which a person or company has a small number of shares in many ships.
Now, the overall value of this market is going to be huge. Quick calculations
show that even in the restricted starship 2300AD the starship market is going to
be at least a Trillion Lv (million million). This is probably larger than the
GDP of America.
Now depending on assumptions the nation willing to sell their tantalum
(Australia) can make a lot of money, several billion livre a year.
At the other end, a nation or corporation which wants to acquire a starship via
the market is going to pay through the nose. Making a hostile takeover bid by
trying to buy up all the available shares (assuming the majority shareholder has
less than 51%) will push prices right up.
Now, I'd like to compare this with the position of western industry in the
1970's etc. when GDW wrote 2300. The great captains of industry had over the
years become minority shareholders in their own companies. The corporate raiders
(led by Jim Slater) noticed this and started mounting hostile takeovers and
asset stripping the companies they took over. I'm going to suggest that perhaps
a simialr thing happened in 2300. Most nations that had starships slowly sold
off shares in their national fleets over the years until they had minority
shares and then had their fleets effectively bought out by corporations willing
to make hostile takeovers.
Furthermore, perhaps one of the more interesting trades would be to make a
hostile takeover of a starship in order to gain the drive. Then strip the ship
and use the drive/ tantalum to build a new ship that can be floated later for a
profit.
This, I'd surmise could be a mechanism for the transfer of starships into
corporate hands.