point one...... dont buy the fluids from your vets office. most vets run the standard mark up and a simple 100ml bag of LRS fluids can run upward of 50$. granted your probably only going to give about 100 - 200mls at a time,that can add up quick. see if you can go through MEDVET (shopmedvet.com)the exact same bag is 2$. the lines are 75cents.you may have to get the needles from your vet though. point two, ask about putting your cat on either royal canan S/O or hills science K/D both are for kidney health.
but thats the easy part. the hard part is deciding when you cat has reached a quality of life issue