Domain For Landing Page

if you want cheap go buy a general fitness domain and install wordpress on it (youtube how to do it, it is easy)

then anytime you want to promote a product just create a different page in wordpress under that domain, or create a subdomain.
Example:

you buy stayfit.com and promote health products.

but you also want to promote a paleo diet ebook so just create the page stayfit.com/paleodiet

If you want to have several different niches then get domain like ereviewproducts.com or something.

Purchasing a domain name and hosting costs very little money. There should be no reason you can't start there. It's more professional.

If you are new to IM then don't make the fundamental mistake of promoting anything and everything. Promote only what you are confident from experience will work for your prospective customers otherwise you will gain a bad reputation and have little or no credibility.

In answer to your question - a separate domain is best for each product or service that you promote. It should not be costly to begin with as you should be promoting only one product or service at a time - and doing it professionally - in order to build up your 'marketing' or 'sales' portfolio for your initial promotions. As you earn commissions from your initial sales, you can invest some of that money in new domain names for further promotions - and so on.

In a nutshell, as has already been suggested, purchase reasonably priced reliable hosting that allows multiple domain names to be used, use a separate provider(s) for your domain names (don't have the same company 'controlling' both your web hosting and your domain hosting), create professional landing pages (one per product or service and domain) and try to legitimately capture email addresses from visitors to your landing page(s).

Captured email addresses can be used to build a list of prospects who can be selectively sent relevant and useful information in order to build up a professional and profitable relationship enabling you to promote additional relevant products and services. Research this latter area of 'list building' on the forum and/or Internet if you are unsure as to what I mean as it will be critical to your business in the longer term.

I hope that the above helps.

You need a domain name you can build a BRAND on.

Think of it as a scalable asset

otherwise, you're painting yourself into a corner.

Having a domain name will build your brand like my fellow warrior rightfully said. Secondly it will make you look more professional. You can use the same domain to promote different niche products is its a neutral domain name that suits all market.

Alternatively you can create a few sub-domains with that same domain for different market

Hope that helps

Don't settle for cheap. Don't take online marketing or starting your own internet business as a "test". Some may argue that the internet *really is* a "tangible" thing. Get serious, and get hosting and domain name from a reputable company, but first do your niche homework first - and first make sure you're up on the latest internet marketing methods.