what will be the approximate budget if I decide to run 100 people sig campaign for a month.
That's already a pretty big campaign, most campaigns we've recently seen are alot smaller.
I'd suggest settling for a smaller campaign, and giving the edge to
quality over quantity.
About your question, it's hard to say, there are just too many other factors besides the size deciding how much a campaign costs.
I can however make a few examples.
Secondstrade (a pay per post campaign, not the best example, but the one closest to your size) pays out around 1
BTC every week, however, that's a campaign with very low rates and many spam-posters.
If you were to run a fixed campaign (I will take rollins rates here for example), that 1
BTC could easily get 20
BTC+, even higher, if we would use the rates of other fixed campaigns.
And that's just pure payouts, not included here are costs for the signature design, the manager, the escrow (if used), etc.
As you can see, costs can vary a great deal, that's why I think it's better to decide a budget first, and then find a campaign style fitting for it, rather than searching a size/style, and then trying to press it into your budget.
Will it be cheaper (or better) than just buying bitcointalk ad after first post in every thread on weekly auction?
Last round, the forum advertising spots went for 1.05
BTC the cheapest. A month would need you to win a spot in 4 advertising rounds, estimating at 4.2
BTC.
Due to the wide range of signature campaigns, that can be either cheaper than running a month of a signature campaign, or it can't be.
About the effectivity, theymos usually posts
some stats together with the auctions.
However, whether or not that is "better" than signature advertising, I can't tell you.
also if I for example will want to pormote a casino that accepts bitcoins, i'm not really interested in a campaign outside bitcointalk gambling section right? can I set up campaign in such way that the posters accepted for campaign will be only (well at least 75% of their posts) posting in the gambling section
https://bitcointalk.org/index.php?board=56.0 ? thanks
Yes, there are ways signature campaigns use for this.
Either a minimum quota of posts that have to be made in that section, or an additional payment for posts in that section, or...
Anyway, you can focus your signature advertising to attract a certain type of poster.