I understand that this project is for 30 articles of word count 400-500 words each. The range of your budget that you have mentioned is $250. I quote only $7 per article for 30 article which equals $210.00 USD.
I will complete three articles per day, not because of lack of inability to write more, but to give myself enough time to research your titles well and make the best possible researched presentation of the articles.
I am an experienced and skilled writer and am found on the net as Amanda Dcosta, and am also much read for my pages Mandy's Pages, which again is viewable online.