The solution for this may be easier than you think - and cost you considerably less than what you're spending on those special foods.
There are lots of easy to believe claims out there when it comes to cat care and food. Incredibly, more research dollars are spent on cat foods every year than on human baby foods! There is a remarkable amount of money made in this industry and while kibble may have it's place, increasing numbers of professionals are recommending against it as a main food source.
Cats are true (obligate) carnivores. They receive no nutritional values from anything other than meat or fish. Commercial products advertising cat foods with greens or vegetables are marketing for the human, not the cat.
Veterinarians who happen to sell high priced, specialized cat foods are usually just joining the marketing aspect of pet care; many vets do not have the understanding of nutrition specialized for different species because it's simply not a big medical school focus.
The best way to start with ideal nutrition is to read ingredients on the cans (yes, canned foods are better overall). Name brands are not important, but ingredients are. Meat or fish should be in the first couple ingredients and not plant products. For example, "chicken, chicXXXXX XXXXXver..." or "beef, chicken ...", you get the idea. Not "chicken by-product meal" "corn meal" , "wheat gluten" or anything along those lines.
Even if you choose a kibble to supplement the canned foods it needs to have a real meat in the first two ingredients. You might be surprised at what could be on ingredient lists of some very popular, very expensive cat foods. Many of these foods are no better (sometimes worse) than dollar store pet foods and what the public would be shocked to discover is that sometimes they both come from the same manufacturing plant, using the same formula and just varying their shape, color or size and packaging.
This was something that became apparent during the recent pet food recalls.
For more comprehensive information on feline nutrition, by a vet who specializes in this research and offers findings and suggestions freely, check this site: http://www.catinfo.org/
Give it a try for about a week - and you may never have to worry about this again. If it doesn't improve, just re open this question (you do not have to press accept more than once on any individual question) - or post a new one - we'll always be here.
I really do think you'll be surprised. Not only at the improvement in the hairball situation, but the defecation overall. Remember to take your magnifying glass though - reading those ingredient lists isn't made easy.
Let me know how it goes.