The coffee chain's 12 oz. (80mg) Americano had the most caffeine overall at 195mg per serving and had the best price per 100mg of caffeine at just Â£1.00.
The cost and caffeine content of a standard 12 fl.oz. cup of Americano coffee was compared by money saving website Voucherbox.co.uk at the UK's most popular coffee shops.
At the other end of the scale Caffè Nero coffee had the lowest caffeine content, which makes it the most expensive outlet in the study at Â£2.56 per 100mg of caffeine.
This is two and half times more expensive than Costa.
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Greggs was the second best retailer for cost versus coffee strength at Â£1.06 per 100mg of caffeine, followed by Pret a Manger at Â£1.30 per 100mg of caffeine and Starbucks Â£1.40 per 100mg of caffeine.
The research also looked into the cost of caffeine in Coca-Cola, Red Bull and a cup of tea, with Red Bull fairing well in the comparison table.
The reason for the variation in coffee levels is to do with the number and size of espresso shots in each serving, the blend of bean used and the preparation method.
The average person should consume no more than 400mg of caffeine in a day and pregnant women should have no more than 200mg, according to the European Food Safety Agency.
Shane Forster, UK manager for Voucherbox.co.uk said: "Many of us have a favourite place for our prized cup of coffee, but if it's a caffeine rush you are looking for it is well worth taking into account the hugely varying levels of coffee strength and considering what you get for your cash at the main coffee shops on the high street.
"Also from a health perspective two Americanos at Costa would take the coffee drinker close to the daily caffeine limit whilst the guidelines permit the thirsty amongst us to indulge in up to five Americanos a day at Caffè Nero if our budget goes that far."