Not the bargain of the year by any means, but Amazon have the Pirelli P-Zero TPU tube with a 60mm long valve for £12.99 each, about half the usual RRP.
Tubey things
I have a few of these, and some of the Ridenow mega cheap ones, and it's fair to say the Pirelli's are clearly that bit better made, not that I have had issues with the RN tubes.
With these Pirelli tubes, they hold, and jeep the air in incredibly well, if they are on a bike you don't use for a fair portion of the year, unlike latex, which loses air as soon you look away, these hold it for AGES, it's very impressive.
The other main plus point, is that they are black and yellow - some TPU tubes have orange valves, imagine having those stuck through your wheel rims on display to everyone
The other more pertinent plus point is that they take up very little space, and also weigh very little versus butyl tubes.
I like to leave the house with two spare tubes, and due to the size of these, combined with using a ride wallet thing (Within which I can fit my phone, keys, tyre levers, multi tool and two of these tubes) I can also now do without a saddlebag.
Across the 4 tubes (2 in the tyres, 2 in my jersey, plus the loss off the saddlebag) it's saved ME over 500g in weight.
Cyclestore & Tweeks sell the repair kits for £5.99, Amazon are trying to knock it out for £12.99!