Let me just say that this is a great thread for adding more politics into Kingmaker. Reading and playing through the AP when it first came out I was a little disappointed with how it skirted around politics. It makes sense considering it came out years before they developed systems like in Ultimate Intrigue and I am tempted to go back in and flavor that in.
I basically utilized bits and bobs from all the posts above to create my series of venture capital listings and I presented them all to my players. Except for some major players (Surtova and the Swordlords namely) most groups offered only 5-10 BP with some having an optional +5BP for an extremely specific request like putting a member of their organization into a specific council position. I can post that all up later if you want but it really is just a rehash of stuff from above.
The big change I made was making the whole negotiation process a skill challenge. I didn't want the one player with the best diplomacy rolling over and over again so I lifted the idea of skill challenges combined with Matt Coville's caveats: You must be trained in the skill and a player can only use a given skill once.
I explained it to my players as that you are at a party with nobles and important VIPs and you are not the only group going around trying to raise capital. Each player can really only engage a single person for a contract (this helped keep the players from spend hours gaming the system for hundreds of extra BP) and each party had a list of 3-5 demands. If you wanted to alter the demands or remove one then it required a skill check (DCs ranged from 15-25 depending on the importance of that request) BUT you can only use a given skill once. You can only flatter someone so much, in my opinion, before you have to change up strategies. This gave me a chance to really push certain knowledges to the forefront so things like Knowledge: Nobility was really important to use with the Noble Houses while things like Knowledge: Geography is great when dealing with the merchant leagues who want to know what kind of resources they can expect from your area. Knowledge: Engineering to impress the miners or Survival to impress outdoorsmen etc.
The only things I added that haven't been mentioned above is as follows:
Aspis Consortium - 5 BP
They want a "Market" (translation Black Market) built within 5 years.
Numeria - 10 BP
They want an Embassy Edict, Chaotic Alignment, Slavery tolerance, +5 BP if you appoint a member of the Technic League as your magister and access to ruins and archeological digs for research and relic study.
Ustalav - 5 BP
I used Esme Currindon from the NPC Guide but she is in disguise as Esme Muralt claims she is a representative of Ustalav but really she is trying to raise a mercenary army to reclaim her county. She offers the funds upfront exchange for a pledge to help her against "peasant traitors" later on. This will end up being a huge expense for the players, at least 2-3 medium armies (might just set a DV requirement) for the span of at least 6 months (a total consumption cost of 48 BP...quite the return on investment!).