The number matters less than the structure. Three pricing models dominate, and they create very different incentives.
On the number itself: in Kolkata, roughly ₹5,000 to ₹25,000 a month buys you a freelancer's part-time attention, ₹15,000 to ₹1,00,000 buys a local agency's production capacity, and ₹50,000 to ₹3,00,000 buys a national agency's process. Our retainers start at $1,500 a month, which sits deliberately above the local bands, because we are staffed for a different job. There is no setup fee, no minimum term past the first month, and never a share of your ad spend.
Be careful with the bottom of the range. A ₹8,000 retainer is not usually a scam. It is a fee that only pays for six or eight hours of somebody's month, which is enough to publish a few posts and submit some listings. It is not enough to work out why Google is crawling forty thousand faceted URLs instead of your two hundred real pages. The cheap retainer is expensive twice: once for the work, and again for the recovery.
The full breakdown, including what a person costs versus a company, is on the SEO expert in Kolkata page.