If I purchase a $40 license to sitecake will I be able to use it on my main and subdomains?
Yes. Sitecake can be used on two locations: test and production.
It can be local and domain. Subdomain and domain. Domain and final domain. Etc
Awesome, thanks for the response Nik! Is there a limit on how many subdomains that can be used with SiteCake?
Sitecake does not see the difference between subdomain and domain. So two.