since i have personally given over 50 oaths it costs over 10 gold most of the time to oath someone, and since you are supposed to help spread citizenship i think you will actually get in trouble for not giving the oath if someone asks for it ( i seem to remember two people getting demoted for not giving the oath)...i got my oath from the warmaster now emperor for free and have given them out for free since then...promotions are a different story...
p.s. also don't get me wrong if there is 6 imperials on and you have already given the oath tell someone else to get off their ass and give it out to someone. Also if it would drop you below acceptable donations levels you should (1. get your gold back up, then 2. give out the oath)
by no means is this anyone's opinion other than mine, and if you want to discuss it more IC then feel fine, like i said just personal opinion
your friendly neighborhood imperial bard