I need to test the market to determine how many people are interested in subscribing to my site. The niche is related to "web design" and "themes". I would like to know if the project I'm planning is worth pursuing.
It will be something like this: on the site there will just be a subscription box stating that if you're interested in what I will be offering to please subscribe. The traffic will be from Google Adwords campaign.
You can use the rule of 1% for approximations. About 1% of your adwords ads will be clicked on. Of those people seeing your home page, about another 1% will click on your subscription link. In order to derive meaningful statistics, it would be nice to target 100 subscriptions. That makes it 10,000 adword clicks. One adword, depending on keyword demand, is at least $1 - $2 (in the US). So $10,000.
If it's too much for you, start the other way: spend $100/day and tweak your parameters/keywords/landing page until you achieve the metrics you care about.
Of course, your mileage will vary.
Remember that this is not a "fire and forget" exercise. As you gather data you should be tuning your :
Tuning them as you go may lower your costs and will get yo more information when you're done. You'll know not only what the market is but messages deliver the best results.
And I suspect that for $3,000 to $4,000 you can get a rough idea of whether there is NO market or there is a market but not of certain size.
More than just one data point
There are actually a few data points you'll want to know about your Conversion Funnel: What is the Click Through Rate for people clicking your ad. And what is the Conversion Rate for people subscribing.
The first might get expensive. Figure testing 20 keywords and needing 100-200 click throughs.So maybe $2,000. But as you figure out which keywords are doing better, you'll get more effective results for that which makes #2 and #3 cheaper.
#2 should be fairly cheap. Your data from #1 should give you this.
#3 Could get very expensive but you'll be gathering data on this while doing #1 and #2 and you will have improved your Click Thru Rate (CTR) by picking better keywords.
Also, when you get #1 and #2 done, you should also be A/B testing your landing page.
If you want to test - you do need to spend thousands of dollars. It is only a test. I would recommend you to start with 100-300 USD per the first campaign. It will give you an understanding if there is a demand on your product/service. And how much you need to pay to drive that demand to your site. Moreover, in the first campaign you will learn which keywords to use to drive traffic and how to overcome your competitors in your niche. The first job you will need to do is grow CTR of your ads (find keywords and apply appealing text of the ad) - way to know to clikc price. If the price is high you will need to look for other ways to drive leads (PR, articles, SEO - very hard for young sites). Start with 0,5-1 USD per click and see the results (impressions and clicks). Then when you find "workable" click price do the math as offered in one of the answers.