I'm quite far into my game already and I'm easily making 18 gold per month, and with some careful saving, I don't see the need for the ransomed money. I let them rot in jail if they are just going to revolt again and I see no pleasure in constantly whacking them.
One of them is spending his 18th year in prison.
Yeah, I guess it's a little different when it's your nobles revolting. I sell off any foreign nobles, guaranteed. I strip the duchy title off traitors and then release them (under new handlers, who usually remove them and take the prestige/relations hit for stripping the county titles for me). Plus, showing some clemency towards the traitors and not straight-up killing them gives you some relations boost which makes more revolts less likely with your other vassals. I did leave my first heir to rot in prison, that guy turned into a monster the moment I gave him his own duchy. The other two are getting there, I'm thinking that letting the AI pick traits always leads to cruel, evil rulers. Next time, the heir is staying in the home country without his own lands.
My income with around 8 baronies is at 20/month, and I knew I could raise 15k before taking the Galician titles (they had maybe 8-10 counties). I'll have to check tonight what my stats are.
You need a better spymaster. Your succession crisis is going to be murder!
My most recent spymaster caught both attempts, and instead of deciding between them I simply gave them claims on each others' titles (because each one has a couple contiguous duchies with a decent-sized force). Plus, I think it was a good RP for the ailing monarch. Fortunately, one of them finally succeeded, so now there's no more succession crisis! Survival of the fittest!