Hi
First of all, the fact that you are talking about market validation is great. I've seen so many startups invest time and money, only to find that no ones wants/needs their product, or that they only want a certain aspect of it, or they aren't willing to pay the requested price. So you're already one step ahead.
Answer: the sooner you validate your product, the better! That said, the version you are validating needs to be representative of the end product, or else the validation isn't reliable. So, what you should do is:
1. create a business model canvas (which is what all startups should start with before creating a business plan),
2. Setup a Wix or Wordpress website (this can be done for free / very low costs). On the website, include the price of the product/service, and enable people to order it (yes, even if it doesn't exist!). I am happy to explain how this can be done even though you don't yet have the final product and by still being fair to the people who click the "buy/order" button.
3. Spend a small amount (say $100 - depending on your budget) validating the idea (promoting the product/service that you listed in the previous stage).
This way, after only spending a very small amount, you will be able to know (if you did it right):
a. Do people like your product.
b. Do people want/need your product (not the same as 'a').
c. Are people willing to pay for your product? (this being the most important stage)
d. How much are they willing to pay? (you can check this by having 2-3 landing pages with different prices on each).
2 additional important points:
a) in order to rule out external factors like an unattractive landing page or advertising campaign, and assuming you have the time, create multiple landing 2-3 landing pages with different designs.
b) during the above process, don't forget to check how much it costs you to get each user/customer to click the "buy" button. If for example each click on your promotion/advertisement costs you $2, and only every 10 people who click go on to the "buy" page, that means each sale is costing you $20. Then check what your average profit per sale is, and then you'll know if your service/product is worth pursuing (obviously there are additional factors like return customers, referrals etc, but you will get a good estimated/validation of the idea/business).
I'm happy to help you with this matter further, as this is a critical stage which if done right can save you a lot of time and money.
Best of luck!