check the overview of signature campaign threads as given by bitcoin revo and before you start your campaign be sure that your campaign can last atleast 1 month so it can get much attention and traffic from bitcointalk users. if you only plan to run for a week then it will just be a waste of money from your side
But i think the duration of sig campaign is depends upon OP if he choose a short period. You can give your own rate based on what is your projected profit in your site compared to the expenses in your campaign. Just make sure you will in profit at the end and don't make your rate above your capacity. Goodluck
Signature campaign is part of a promotion to introduce your site to the public and do not expect to benefit in the early promotion
Almost all sites suffered losses when the promotion it's a natural thing after public know about your site they will come if you offer good services they will use but do not expect if your bid is equal to another site or even worse.
For the price usually if you do not have a competitor you can offer low prices but when many competitors like gambling you have to offer a higher price.
