One of the domains .us is for sale what would be a ball park figure to buy such a domain?
I made an offer for a domain recently and they told me they were only excepting 7 figures offers and that they had turned down a 6 figure offer. So really it is up to them.
If the org has their name trademarked they may be able to get it through legal avenues but there are many factors that play into this.
It's called Domain Name Dispute Resolution.
[arbforum.com...]
[arbiter.wipo.int...]
There is more info here.
As the the value of the .us domain. It entirely depends on the name. If it's something like redcross.us (a household name) it might be worth up to tens of thousands in value (or even more). If it's more mundane, it might be worth only hundreds.
As for the strategy to buy it? How much is the organization willing to pay for the name, considering there isn't anything else available? Probably thousands. You should approach them as wanting the name for yourself, not representing the organization, (it's easy to transfer later) and offer a high hundreds offer. Take it from there with the negotiations.
Another option would be to maybe go with their initials, or something similar or catchy, and then brand the name to the organisation with PR.
As I said at the beginning, if the organization want's that name and no other, they gotta buy them up. They will lose traffic to the other .tlds and they might not want to have them fall into the hands of a porno operation. Which could be extremely embarrassing for them. It might be better to go with a new domain name where they can register all the major .tlds and then brand the domain to the organization. Branding doesn't come for free, it requires PR. Both options might cost about the same in the end.