I Own a Blog on Tumblr.com that post streetwear/clothing pictures. I currently have over 40,000 Followers and gain average 1-2 thousand followers each week. I post twice a day on average, and the posts can get anywhere from 400 to 14000 "notes" (Likes and reposts). I received an offer from a clothing company today that asked if i would put a link to their website on every post, for a flat-rate monthly payment. they offered me 30$ a month to start. I think this is very low but i have no clue the worth of each post. the posts can get exposure of up to 500,000 views. How much should i ask for?