In order to enable https for a website you have to use a ssl certificate. Now we have free SSL certificate offered by "lets encrypt". You can get it free and setup with just a click in cpanel of most hosts including stablehost. If your looking for a professional level ssl and company level verified ssl, then you can buy at low cost from namecheap.
If your just looking to get https, then free ssl from lets encrypt would be fine. For basic payments etc, any domain or company level certificate would be fine.
Free ssl will be avaiable via cpanel of most host. Specially it is free via stablehost cpanel ( via let's encrypt plugin in cpanel ).
You can get domain or business verified professional positive ssl and comodo ssl from namecheap starting around $10 onwards.