If there's one surefire way to get the worst return on investment, it's by underquoting a SEO client. And the reason for this is that SEO is an ongoing competition. It is a search engine race where your goal is not just to reach the first position but to stay ahead of the pack.
If you estimate how many people are ahead of you, you will know how fast you have to run to stay ahead of the competition. If you keep running at the same pace, you'll never be able to match the pace of the competition.
How much you invest in SEO will ensure your speed and your ranking in search engines. Do you want to get faster? So, invest as much as possible. The more you investment, the more time you get. Think of it a bit like a personal trainer, the more time you spend with them, the more you improve.
If you are investing ₹2000 per month on SEO strategies and those ahead of you are investing ₹6000 per month, how can you get ahead of them. You can't. It is important to calculate your current speed and invest accordingly. Only and only by doing this you can guarantee your results.