Just have to chime in here as we are also dealing with chronic renal failure.
First, join the CKD group on yahoo-
https://groups.yahoo.com/neo/groups/Feline-CRF-Support/info
Second, this is an incredible source of information for Renal Disease in cats:
http://www.felinecrf.org/index.htm
Feline crf.org also has a food list that will list available foods by phosphorus level. Always give phosphorus binder with each meal. Higher phosphorus levels further damage failing kidneys.
You can give over the counter B12 and B Complex. I use Solgar brand from a health food store as it has no sugar (methylcobalamin is the best). B12 is 500 mg and B Complex is 1/10th of a human dose. Just mix the powder in with the food once a day. With renal failure there is always the risk of developing anemia. By adding B12 and B complex you can help prevent this.
You don't have to use TumilK, we were using a supplement that was 468 mg per dose.
See if your vet will give you an Rx for the fluids, they are much cheaper online. My vet was charging $28 per bag but I found an online source for $5 per bag. So now he price matches and I save $23 per bag. You can also save a quite a bit of money by purchasing your admin sets and needles online as well.
As for the phosphorus binder, if you are getting this from your vet you can also obtain the powder less expensively online. I got a one pound jar and have been using that for a year.
Diabetes can be expensive enough but with the added issue of renal failure it can be even worse. But there are many ways to cut the vet expenses associated with renal failure and keep your kitty relatively healthy.
You did nothing to cause the renal issue; it is an unfortunate eventuality that many cats experience. I urge you to visit the website of felinecrf.org. It is really an invaluable resource.