TBH suggest you dont bother, £200 is not a lot for a custom loop £300 is where you need to be really, By the time you pay the shop to fit it. (this would likely be quite a bit as it takes time to fit a custom loop) you looking at £300 for a £200 loop = very bad value.
Just fit a H105 cooler available from here if you want "watercooling"
Dont forget a custom loop is not maintenance free and it sounds like this is what you are after. The H105 is water cooling thats maintenance free.
Custom loops are really designed for people who want to fit it them selves so they can maintain it them selves. Also if 3 months down the line a fitting comes loose and water going all over your rig and does loads of damage are you expecting the shop to replace your hardware ? they wont. i really would suggest doing this yourself with good components or just stick with a all in one cooler such as the H105