you numbers are confirmed by steemd. here is a brand new (3 days old) account:
https://steemd.com/@jimmyjamjar10101

Also, in testing yesterday I posted 2 comments. a longer comment cost me 24Billion RC, and a shorter one cost me 19Billion. so, while steemd's vote estimate is close, the length of your comment will also significantly affect how many comments you can post. Get ready for 'tweet' style comments as opposed to actual engagement (this comment is probably going to destroy my RC)