Zero. There is no substitute from the insight you will personally gain researching your own market. You will never get a transfer of situational knowledge from a service bureau doing your primary research. This is an essential part of getting to know your future customers. If you aren't doing it, you're going into a market blind. Data is flat, it has no personality. Being able to get the raw information and synthesize it into a report means you learn the nitty gritty details of your target audience and have the greatest connection to your customer.
Never give this power to someone else. It's an extreme risk to be ignorant of your customer by farming this task out.
Now once you have done your primary research, there's nothing wrong with a service bureau repeating your research with a larger sample. But never have a third-party do the first round. You won't know if the questions are the right ones unless you ask them yourself. You won't know what they aren't telling you if you haven't had the interviews or questions go off the rails. A servicer will only perform the task in front of them. They won't think like you. They won't understand the effect of the answers. They cannot adjust the questions. And they won't know what they should have asked but didn't.
We have paid as much as $25-30K for a very thorough, customized and referenceable analysis by an independent consultant or other expert. If your market is emerging and/or not well understood by investors, or if you are seeking capital from family offices, this analysis - specifically from a third party - will be extremely helpful in getting investors and executive/cofounder hires over the finish line.
Third party research organizations often provide sizing as a part of a larger industry study priced between $10-15K but you need to screen these organizations carefully to make sure they truly have depth in your market area. If not, buyer beware. You can ask them for sample report pages with the data redacted to ensure its something you can use.
It depends on why you need it. If your concept is based on your own user or customer perceptions and insights (buy side) but no experience making or delivering the product or service (sell side) then you probably need help understanding the industry you're going to be competing in. If you've been on the sell side then you should tackle this yourself.
Before paying anything see what's out there for free. If you're entering an industry with public companies in it, many of them post their own investor and analyst presentations online. You can open an account at one of the big investment houses such as Merrill Lynch (not a discount broker) and then ask to get copies of their analyst reports.
Depends upon how much value it is to you. If an investor needs a third party to validate the addressable market, then it's probably quite valuable to you. And if it is done from the bottom-up based on a thorough analysis (original sourcing, interviews, surveys), it would not be unreasonable to spend $25K or more. Definitely ask about the process and deliverable before committing.
But if all you are looking for is validation for an idea, then I would not spend much and validate it on your own... engaging prospects, speaking to people in the market, etc
As a founder? Very little. If I am doing basic market size validation research it is because I do not know if it is worth spending any money on the idea.
It would be magic if it replaced hours and hours of research, but I'd much rather have the right primary source material.
I think very little in an early stage startup, which is a shame considering it's essential at this stage.
Funding for startups aint always readily available, hence, in as much as it would be wise to spend good amount of money acquiring data and analysis on the market size of a product especially at an early stage, its often difficult as its down the pecking order in a scale of preference.
I don't have much capital. But am committed to making money. I wish I can work with you.