Base on the description of your needs, a free account from efax.com should work great for you.
I have used both software based and Internet fax programs through the years and have been pleased with their performance vs clunky fax machines. There are some intangible benefits to consider with the Internet and software fax systems. Since they are paperless, fax storage and tracking is simple and easy. Paper faxes always seemed to end up on the corner of my desk in the never-ending "To be filed" pile. :) Another great benefit available with Internet based systems lets you send and retrieve faxes from any computer that is connected to the Internet. This feature is great for those who may travel.
There are several highly rated software programs that you can purchase depending on your needs. Winfax is a good one that I have used, although it was five years ago when I used it. Since then I have chosen the to use the internet based fax solutions. Most of these services offer free local telephone numbers and free faxes (certain limits apply) for personal use. This solution is ideal and economical for those who don't use a fax very often. Efax.com is the service that I have used over the last several years. I have used both the free accounts and the paid accounts and have been well pleased with their service.
If you decide to use a software based fax solution, you must have an available phone line in most cases. This could add to the overall cost of the system. Internet based systems do not need a phone line to be available, but you get a local number from the service. Toll free numbers are also available with paid accounts. This is a great advantage for small businesses and startups because you get the benefit of looking like a much larger company.
If you find later that you are sending and receiving a lot of faxes, you may want to reconsider the available solutions. There is a point where it makes good business sense to at least reconsider the available solutions. As your fax needs change, it may make good financial sense to go to a self contained in-house fax server using an available software program, upgrade your internet based service, or invest in a high quality fax machine from an Office systems supplier.
Good luck and I hope this helps.