If you've not heard of it, Gfuel is great. They do a Lemonade Flavour variety. I drink it a lot, you can buy a tub of it that contains 40 servings (powder) you just mix it up and go. It's sugar free and not too sweet either. The tub may be expensive for one purchase but it comes out at about half the price of a regular can of Monster or Relentless per serving. It's also apparently better for you as there's more natural ingredients in it. They've got a promotion on their website at the moment to buy one tub get one free. I know the site is American but they do ship to the UK and I've not had any issues getting it shipped here. I think you can also find it on eBay too. Hope this helps!