SEO starts from just Rs.15,000 per Month. Minimum 4 to 5 months will be required to get your site link at the top with guarantee.
But, it also depends upon the key words and the market competition that how is your competitor is doing SEO of his website. So, the time variation depends upon your market niche.
Likewise, the time for to stay your link on the first page is also not confirmed. It may possible that it can last for months and even for one day only. Means SEO is a regular process. If you will have the SEO of your website regularly then definitely it will stay first page of Google whenever that particular keywords will be searched.