Hello,
Yes, it is necessary to remove the Not Secure badge. Commercial SSL certs range in price from $50 to $250+ per year depending on the vendor, encryption level, etc.. Many sites don't really need them, but if your are doing E-commerce, then it would probably be best, as many folks won't do business without a secure connection.
GoDaddy currently shows one website for $63.99/yr, $79.99/yr at renewal. If your domain and site are through GoDaddy, that would probably be the easiest.
C