The hyperactivity and always wanting food could also suggest HyperThyroidism, have the vet run a full blood panel with T4 add-on.
HyperT and CRF sometimes happen at the same time and when the HyperT is controlled you have a better idea of what state the kidneys are in.
Have a good talk with the vet about treatment options, with tips learned over the years things don't have to be as expensive as first thought.
For example buying sub-q fluids and supplies from licenced pharmaceutical supply companies or your local pharmacy is significantly cheaper than buying the same supplies from the vet
Learning how to give sub-q fluid injections at home is far cheaper than going to the vet to have them administer it. Depending on the fluid requirements a sub-q fluid schedule at home is cheaper than IV fluids at the vet.