Not sure how it is where you live but over here (Germany/Switzerland), 7/16 (or around 11 mm ID as we would probably call it) is not all that popular I think (this is of course based on extensive market research I have personally conducted and is 100 % reliable data

).
At least I cannot remember when I've last seen it in a build log on one of the German forums.
When watercooling started out here, most people used 8/6 mm or 10/8 mm tubing, and nowadays I see mostly 16/10 mm, 13/10 mm and 16/13 mm (again, this might be different where you live).
So, if your situation is similar, my advice would be to switch to different tubing diameter. 16/10 is a nice balance between not too bulky and high kink resistance due to having strong walls and has served me nicely. 16/10 compression fittings also have the advantage of fitting on most components (they're not too bulky) and coming in a very wide variety due to their popularity. Your needs/wishes might of course differ.
As for cost, fittings are sneaky fuckers in that regard. You can quickly add up 100 to 200 bucks' worth of fittings without a problem. This is especially so for nice compression fittings. But that's just the way it is. If you're in the business of saving money, water cooling is probably not the sanest of choices
