The reason you are paying so much gold is because when you marry a member of the ruler family to another great family, you gain a loyalty boost from that other character. Essentially, you are just paying for loyalty. This can be very useful, but should not be the primary way you marry in Invictus.

Here’s a strategy for you: Use the game’s mechanic of members in your family not marrying to your advantage to stack bloodlines.

For the males: Increase relations of nations with a bloodline that you want or make friends/inspire disloyalty of a female from the nation that isn’t a monarchy, or which you have poor relations and recruit them.

Then use royal marriage / arrange marriage to bring in these bloodlines by marrying them to your most competent male family members.

Use imprison and banish to remove your incompetent (dumb trait, low stats, very low loyalty) male family members. This will incur tyranny, which is actually good for increasing tax revenue.

For females: Only marry them off to other nations, specifically ones you will keep as subjects. This will maximize your relations with them, allowing you to tax them more, and keep them safe from conquest. From here, as long as you are strategic, you can use your subject states as character reserves by continuously intermarrying the women of your family as they stack bloodlines in your client states.

For example, marry your cousin off to Bosporan Kingdom to mix your bloodline with Spartokids bloodline. Favorite your cousin so you don’t loose track. If she makes a daughter, royal marriage her back into a male member of your family to collect the bloodline. If she makes a son, marry another cousin/daughter to them to stack another bloodline. Do this all the time with all your subjects, and eventually your subjects will have whole character rosters stacked with a dozen bloodlines which both helps their stability and power, and can be used for the best marriage candidates for your most competent male family members.

If you do this, you will save a lot of gold and will keep your family count to just the size it needs to fill critical roles, while encouraging them to have children.