How can i buy scope for a one off survey for 150 people?

Hi,

My apologies, I am not sure what you are referring to.  Could you please elaborate a bit more on what you mean by "buy scope"?  If you are simply looking for a slightly more submissions than a Free accounts provides, there are several "Get More" tasks you can do in your account settings:

https://www.jotform.com/myaccount/getMore

If there is something else you need, let us a know a bit more detail and we will be happy to help.