The basic maintenance costs are set in settings.txt, unmodded it is 25%. If you setup your race with characteristic "maintenance cost", e.g. to 110, then you will have to pay 15%, if you additionally take a cultural modifier (merchants for example with 5% maintenance reduction) then you will end up with 10% maintenance costs. And then there are the chrystalline races, with some nice facilities, which... Give it a try...
There is also a lower limit, you cannot go below 5% (hardcoded).