My cat is sick -- any advice?

I had a cat about 6 six years ago who was sick for about a week and I waited to take him to the doctor till Sat, and he died Fri evening. So one of my cats now is sick, and I'm not sure what I should do. I don't want to jump the gun and put him through the torture of going to the vet and paying the astronomical fees that my local vet charges, if it's nothing.

He's threw up his cat food and then has been throwing up like somewhat clear white liquid, but not much at all. I do have a new cat food, and I put some flowers out that I think he was eating. He's not acting any different, he's not lethargic or out of sorts (as my other cat was), so has this happened to anyone else? Any suggestions? Should I wait a few more days? Take him in? Help!