Individual domains and subfolders have their own benefits from SEO and business point of view. If you create separate sites for your different services then you have to optimize all sites accordingly. Having separate sites for different service may help you to optimize your websites properly but you can do the same with a single domain by using sub-folders or subdomains. If you put your all effort for an individual site then that site perform well instead of doing similar job for 4 sites, it also quite cost effective.

So it is better to stick with a single domain and there you can use folders (yourdomain.com/xyz) or create subdomains (xyz.yourdomain.com) for different services. Google also uses Subdomains for their different set of services, for example maps.google.com, news.google.com and blogsearch.google.com. Each of these Subdomains has their own content and focus on different services.
Instead of cost effective, Subdomain or sub folder also helps you in other terms. Like -

  • It is quite easy to handle one single website instead of 4 websites.
  • If your visitor enters any of your subdomains then they can easily find out your other section and your main website.
  • If you are going for a sub folder or subdomain it will yield better results. Search engines will distribute ranking power among other pages on the subdomain including home page. If your subdomain is popular and receives plenty of links, then your main domain will benefit from the activities on your subdomain.

So it is better to create separate subdomain for your different services.