Hi, my name is Kamil and I run Survicate. It's not as simple as you say and pricing for a survey software might be actually one of the most challenging ones.
First of all there is always a minimal cost to serve a customer. In our case we offer 24/5 livechat support for all, and even customers who collect 50 responses might use our support extensively in some cases.
Then a response (submission) in one survey doesn't cost the same as in others. To really flatten the cost you'd need to create a pricing based on 'an answer to a question', as a response is a row and an answer is a cell. So a survey with 50 responses and 50 question cost more to store and process than a 3 question survey with 500 answers.
But it's not about the number of questions only. Most of customers identify their respondents with merge tags or pass additional user attributes via js they can use to filter results - every single attribute counts as you'd count questions, that's yet additional cell.
But that's not all - in case of Survicate we offer targeted in-app (saas, mobile) and website feedback surveys that require a tracking code to run. That generates cost (CDN) even if you don't collect any responses, and if you put it on a high traffic website to run short surveys, the cost of a response must take into account the traffic cost as well.
But we're not even half-way through yet :)
In case of one-time off surveys the number of responses you collect in a month really doesn't influence the cost that much. But you analyze the survey - the more responses, the more questions, the more to compute. So an NPS survey collecting 1k responses a month is a 12k responses survey after a year - so everytime you click 'Analyze' the cost is 12x+ higher than in the first month. The more often you analyze, the higher the cost. We offer unlimited users - curiosity multipled ;)
You want to be up-to-dated with results, so you enable reports to get emails with new replies - that's again grinding through all the responses daily.
You want to act on feedback, so you connect Slack, Hubspot, Google Sheets - not only that generates additional cost.
Having said that - we're cooking a pricing change that will address the issue of the irregularities in responses volume you mentioned.<p>And yeah, surveys are super valuable, and if you weight the value of feedback you get against the cost, it's peanuts.
Stay curious and dare to ask ;)<p>Kamil