Some of this might be old news to you, or you may find some useful info in there. In any case here it is. If I am able to help one person, that would be great.
The first thing is to have identified at least one possible niche you want to research. The method will give you an idea if the niche will be profitable or not.
So lets start:
(Disclaimer: none of the links I provide are something I'm selling or I am an affiliate to, they are just market research resources)
Head on over to www.QuantCast.com
QuantCast is a ranking service kind of like Alexa, but will show you things like demographics and other websites that visitors go to. Research your closest competition and also any cross competition (i.e., companies that target the same market but with different products or services than yours). Get an idea of their monthly visits, demographics (age, income, race, gender, education).
Double check the monthly visits with www.Compete.com which will also show you their top 4 or 5 keywords that drive traffic.
After taking notes head on over to www.Omgili.com
Omgili is a message board and blog search engine. Research the keywords you are trying to use to access message boards like this, where people get together to discuss problems. See what your customer base issues are, learn to speak their language. See what they want out of a product and take notes so you can create your product to solve their problems.
Do the same with www.Boardreader.com
Go to www.Facebook.com, sign up for an account and do a search for Groups that have to do with your niche, etc.
Do the same With Google Groups.
Again, see what people are saying that post on these groups.
Facebook will also tell you the size of their groups so you can get an idea of the size of the market.
Go to Google Keywords and do a search for the monthly uses of your keywords, and see what the competition is.
Go to Google Trends search your keywords and see what regions of the world your keywords are most searched for. Keep in mind that Google trends is a relative traffic counter. I.e. it will not give you specific number of visits. However, if you type in two keywords or phrases separated by a comma it will compare both. If you know the monthly traffic of one of the keywords you will get an idea of what the traffic for the other keyowrds is by comparing the graphs. Again pay attention to what regions, states, cities and countries your keywords are most searched in.
Now that you have gathered some info, head on over to www.Weebly.com and create a quick sales page. Include graphics, videos if you can, do a regular sales page as if you had a product. Create another page called Order and have a link to it if the visitor wants to purchase the product. On the Order page, you can say that your product is currently on backorder, but will be available soon. On the Front page create an opt-in form which will forward signees e-mails to your e-mail. Promise to send a FREE report, a recepie or something else to entice them to opt-in. I would also suggest that you create an optin form on your order page as well, so people interested in purchasing your product can opt in to be notified when it is ready. To keep both separate maybe forward to a different e-mail address.
Sign up for Google Analytics, and paste the code into your Weebly page. To do that go to Settings, and there will be a field where you can paste the Google analytics code, so you can track your visitors, what keywords they use to find you and if they click on the order page.
After you have done a satisfactory job with your FREE website, create a blog on word press and write several posts, each at the end linking to your weebly website.
Write a couple of articles on www.EzineArticles.com with a link on your Profile to your website.
You can do several other things to drive some free traffic, but if in a hurry, I'd say spend $40-50 with Adwords to drive traffic to the test page.
Monitor your visitors until you reach about 100-200 uniques. Monitor the time they stay on your website, monitor if they click the Order page. Once you have gathered a good sample, calculate the conversion rate. The average conversion rate for the INet is 2%, but with a highly specialized and niche product it can go up to 15% or more. I'd say that you would be doing good if you have a conversion rate of 5-7%.
Do some split testing, see if your page can be tweaked until you get a good conversion rate. Then you do some calculations based on estimated monthly traffic and your conversion rate, and you see how much your ROI is. Then calculate if the niche will be profitable.