This is one of those "the ai has different rules than the human" moments that plague the game. Like asking for starbase removal or peace terms.
Generally, when asking an Ai to go to war, it will cost the player at least 3000cr in "stuff", whatever that may be. Modified by relations, power, etc etc, mostly upwards.
When an Ai asks a human, they offer 1 tech (usually the lowest end one you don't have) or 10% of their treasury (max) or 150 cr whichever is higher. And there IS no option to negotiate.
So, if the game is going to assign value to requests like that, which it should, those values and rules should apply to everyone equally. It's a simple matter to code and fix by just increasing the value of stuff offered and making it like any other trade deal. No new mechanics involved.
Don't hold out hope this will get fixed soon though. Diplomacy is getting reworked in the expandalone, so odds are it will get fixed there for $ rather than for free now.