I actually explored Ring Central for a client a few months ago. She only needed one line. Their pricing is based on number of users and for one user they quoted me $35/month if you paid by the year and $50/month if you pay monthly.
We have been using skype for quite some years now and plan to use on our new business you can use your headset or have a telephone that connects to your wifi so you dont have to be logged on your PC you purchase a phone number and pay quarterly for the phone number but it is inexpensive (£14 per quarter) then allows you to call landlines and landlines to call you - they have free answerphone service also so if you are not on line answerphone will pick up. We are based in Spain but aimed at UK Market so I opted for a UK Number so people are not put off by the telephone number being Spanish