You can buy a whole jar of sucralose in the supermarket for £1 and just dilute it with water. However, it burns and ruins coils more than stevia so I've now switched to stevia powder for sweetness.
Cool, i don't like the bitterness you get with stevia. I wouldn't have thought small doses i'e 1 drop per 10 ml should really affect the coils too much. I make my own anyway so I'm not too bothered. Thanks for the heads up though.