VOIP.MS’s setup can be a little challenging, but their service department (Chat or Email) is great. They also have really good setup guides to assist you as well. In terms of cost of VOIP service, I’ve spent about $15 for a phone number and phone service with e911 since Feb 2018. Or roughly $2.50 a month.
https://www.amazon.com/Cisco-SPA112-Port-Phone-Adapter/dp/B00684PN54

