Get Online @Home is also offering a £74 laptop with the same broadband costs - providing customers take the offer between June 11 and June 30.
Both include Windows 7 Pro with Microsoft Office Basic - which have an estimated retail price of £150.
Get Online @Home is an initiative from Microsoft and its partners to provide low cost refurbished desktop and laptop computers to support the Go ON UK digital inclusion programme - a push to improve Britain's digital skills.
According to the company behind the offer, 16 million Britons still do not have basic online skills, and 800,000 of the most disadvantaged schoolchildren do not have home internet access.
Chris Williams, at Get Online @ Home, said: "We are delighted to be able to make this extraordinary deal available to offer real help to people that need it. Never before has anything like it been made possible and we know it will benefit all those who have previously not been able to get online."
Supporters of the offer say it could help get Britain booming because at least 75% of jobs now require online applications and the Government wants 80% of submissions for universal credit to be online. Savings of £3 billion a year could be made if the digitally excluded shopped online, Get Online @Home said.
The offer coincides with the start of the National Digital Inclusion conference in London which is being held to discuss the role technology can play in transforming the nation's skills, businesses and government services.
Since launching in 2011, Get Online @Home has supplied more than 23,000 computers across the UK. All the refurbished PCs and laptops are designed to do the basics well, with minimum spec of 60Gb harddrive and a 2GHz processor.
- Grandmother jailed for £75k benefits fraud
- Coalition to slash benefits again?
- Job vacancies increase, says report