The FTSE 100 may have an uncertain future, but its long-term return prospects appear to be relatively attractive. Low interest rates mean that cash and bonds lack return potential in many cases, while buy-to-let property returns could be negatively impacted by factors such as rising unemployment.As such, now could be the right time to buy a diverse range of large-cap shares while they offer good value for money. Here are two FTSE 100 stocks that appear to have wide margins of safety. They could be worth buying today with £5k, or any other amount, to improve your prospects of retiring in comfort.5G is here – and shares of this ‘sleeping giant’ could be a great way for you to potentially profit!According to one leading industry firm, the 5G boom could create a global industry worth US$12.3 TRILLION out of thin air…And if you click here we’ll show you something that could be key to unlocking 5G’s full potential…Sainsbury’sThe recent results released by FTSE 100 retailer Sainsbury’s (LSE: SBRY) showed that coronavirus continues to have a major impact on its sales performance. For example, in the seven weeks to 25 April, the company reported a 12% rise in grocery sales. However, this was partially offset by a 53% drop in clothing sales, as consumers adapted their spending to lockdown measures.Looking ahead, it would be unsurprising for similar trends to remain in place over the coming months. It may take time for consumer confidence to improve. And this could mean that demand for non-essential items is relatively sluggish.Despite this, Sainsbury’s appears to offer a relatively sound long-term outlook. It has invested large sums in its online capabilities. This could mean that it is well placed to capitalise on high demand across the grocery, clothing and general merchandise segments online.Furthermore, the FTSE 100 retailer expects the higher costs it has experienced in recent months to be partially offset by business rates relief. As such, it could offer good value for money after its 12% share price decline in 2020.FTSE 100 miner Rio TintoAnother FTSE 100 share that could offer long-term capital growth potential is Rio Tinto (LSE: RIO). The iron ore miner’s recent update highlighted that all of its assets remain operational. And it said demand for iron ore has remained robust across a number of key markets.Demand has continued to recover in China, while the company reported that the outlook in the rest of the world is more uncertain. As such, weaker commodity prices could be ahead if demand proves to be softer than previously expected.Rio Tinto also reported that industry supply costs have fallen over recent months. For example, lower energy and freight costs could help to maintain its financial performance over the short run.In the long term, the company’s sound financial position and its high-quality asset base may mean that it can produce improving returns to investors. Although its share price has bucked the wider FTSE 100 downward trend in 2020 to rise by 12%, it could continue to deliver capital growth as the world economy’s outlook improves. Therefore, now could be the right time to buy a slice of it. Why I think £5k invested in these 2 cheap FTSE 100 stocks could help you to retire in comfort I would like to receive emails from you about product information and offers from The Fool and its business partners. Each of these emails will provide a link to unsubscribe from future emails. More information about how The Fool collects, stores, and handles personal data is available in its Privacy Statement. Simply click below to discover how you can take advantage of this. “This Stock Could Be Like Buying Amazon in 1997” See all posts by Peter Stephens Click here to claim your copy now — and we’ll tell you the name of this Top US Share… free of charge! Peter Stephens owns shares of Rio Tinto. The Motley Fool UK has no position in any of the shares mentioned. Views expressed on the companies mentioned in this article are those of the writer and therefore may differ from the official recommendations we make in our subscription services such as Share Advisor, Hidden Winners and Pro. Here at The Motley Fool we believe that considering a diverse range of insights makes us better investors. Our 6 ‘Best Buys Now’ Shares Image source: Getty Images Enter Your Email Address Renowned stock-picker Mark Rogers and his analyst team at The Motley Fool UK have named 6 shares that they believe UK investors should consider buying NOW.So if you’re looking for more stock ideas to try and best position your portfolio today, then it might be a good day for you. Because we’re offering a full 33% off your first year of membership to our flagship share-tipping service, backed by our ‘no quibbles’ 30-day subscription fee refund guarantee. Peter Stephens | Tuesday, 9th June, 2020 | More on: RIO SBRY I’m sure you’ll agree that’s quite the statement from Motley Fool Co-Founder Tom Gardner.But since our US analyst team first recommended shares in this unique tech stock back in 2016, the value has soared.What’s more, we firmly believe there’s still plenty of upside in its future. In fact, even throughout the current coronavirus crisis, its performance has been beating Wall St expectations.And right now, we’re giving you a chance to discover exactly what has got our analysts all fired up about this niche industry phenomenon, in our FREE special report, A Top US Share From The Motley Fool.