the cheapest i found when looking in the market is segotep halo blue around USD40 but i cant find it in ebay anymore... i bought 2, one as spare in case i need it in another system..
talking about tube leak, i believe there should be always a way around. hardware store should supply few compatible pvc/silicone tubing that can last much longer, and also longer in length if required such as external mounting etc. adapter can also be made/bought easily i believe. i prefer the transparent tube so i can see liquid circulation inside, if rust developing, water pump not working etc, but my water cool is still new so maybe next time for the mod. looking how tough it can cool my old power craving 95W cpu, i believe water cool is only necessary for gamers. if no other good reason, air cool will be sufficient to avoid unnecessary leak/clog/dead pump risk. i put it in my system just because the upgraded cpu will only require larger air cool heatsink that cant fit in the tight space. so i have to bring the heat far outside the area hence the need for the water cool. arguing about the heat dissipation capacity, if you are too afraid that it wont be sufficient, just buy the 2 or 3 fans in the pack, like Simon's linked but £100+ is not something i'm willing to spend, even a single fan is rock solid enough for my need. Segotep also comes with double fan setup..
and few other brands come with cheap price. so this is not for a premium grade users only anymore... leak is not the only risk, clogging, rusting also are, seeing whats inside maybe can give better clue if you want to take the risk/mod effort... open loop system also available in tank like setup... you should also aware of thermal mass nature of it, ie when the water heated up due to longer PC usage time, it will takes time to cool down. not really an issue as long as it can be dissipated more than generated by the CPU... equilibrum will take its place...
ymmv.