Aw, Cinnamonmon - I really feel for you because senior pets are definitely expensive - and then you have the younger one with other issues that you weren't aware of.
I wonder if any of the vets in your area have office plans - i.e., where you pay a monthly fee and in return you get free office visits and some free services as well. More and more vets are offering these plans - which are kind of similar to what Banfield offers. I know Banfield is not often the best, but maybe they would also be an option for you? But, in an emergency/after hour situation - that doesn't help, I know.
Lastly, sometimes you can come on here and ask for guidance as to whether you "should" go to the vet - but, none of us are vets here and none of us can see your baby - so all we can do is give our best guess over the internet with the info you provide, so there is always a risk there, but I know people really try to give good advice.
The link that Deja Vu provided is GREAT
and I'm going to put it inside one of stickies in the Emerg. Forum.