Perminant Backlinks & Twitter Promotion

Hey everyone!

i've been making money online with twitter for like maybe a year. Im earning from adsense and ebay (EPN) affiliate programs...

I was thinking of making a service for people looking to advertise their site on all of my twitter accounts pertaining to their sites niche, and a link to their site from my site.

What would a good price be to charge per submission(s)?

Site Traffic = 20,000+ views per day
Twitter Accounts = 3,000 w/ an average 5,000 followers.

let me know what you think. thanks!!

I forgot to mention that the submitted link from the user would be constantly tweeted on twitter, as it rotates through other submissions.