Agreed on the tenore, they are fantastic.If £20-30 is the max, then I would get the Pistons.
However, I agree that if you can increase your budget to £33, Zero Audio Tenore is much better and is excellent for dubstep, pop and dance because it has tight, punchy bass.
http://www.ebay.co.uk/sch/i.html?_odkw=zero+audio+tenore&_sop=15&_osacat=0&_from=R40&LH_PrefLoc=2&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xzh-dx200-ct&_nkw=zh-dx200-ct&_sacat=0
But if you're set on the 20-30 range and you're going to listen to bassy and electronic music, the piston 2.0 plays it very well and is a great entry into quality iems. I almost want to say that you might enjoy the piston 2.0 better than the tenore because it is a more consumer friendly sound with prominent bass crisp treble and a v signature, they have awesome packaging, and it will give you a base to start asking questions when inquiring about your next set of iems. Pretty much everyone here has a pair of Pistons and will be able to describe and compare and contrast them to what you are inquiring about in the future.
I say this because once you buy your first set, there will always be a second, and a third, and a fourth, and on and on...
Hence the "sorry about your wallet"