no, that doesn't matter. You could as well use the new "Let's encrypt" extension, which makes it pretty easy to get certificates free of charge to reach your goal.
even that it is "experimental", it works as expected and without any issues ( I use it now for 2 month now on different production servers, with quite a lot of domains and subdomains ).
for commercial options if you buy a cheap one, yes you gone need to buy 2 ssl.
there is another version that enable you to protec domain and sub as i remember they call Wildcards ssl.
frequently is more cheap to buy 2 ssl than one wildcard.