It depends on how many of us and which altcoin you are talking about... The key to a pump and dump scheme is not only to pump the price up but create hype before and during the pump to make others FOMO into it if you want the profits.

As for the pump a very small coin can probably be pumped for $1,000, a medium sized one for $100,000 and a top 10-50 one would require millions.