I think I would lose it if I actually worked out the numbers.
I just came from the pet store - went to get kitten food, came home with a bunch of toys and treats on top of the kitten food! Spoiled rotten little furbabies!
I have to buy cat grass every other week, I think I spend more for food in a week on the kits than I do for myself, LOL, and I only have two! Not to mention toys, treats, vet bills, brushes, petromalt, filters for the fountain, kitty litter, etc., etc., etc...
I think it is VERY responsible of you to think about rehoming a cat if you think that keeping it will put you over your means. Others might say that they'd give up their home rather than give up their furbabies, but I think that you have to be realistic and do what is best for yourself, FIRST, or else you can't take care of anyone or anything else.
You have to do what you think is best for all concerned. However, I DO have to ask, is it a dollar issue, or is it simply that you like the new kitten less than your older cat? If you are using the money to rationalize your decision to rehome the kitty, I'd say go ahead and find him a new home, and be honest with yourself about why exactly you are doing so.