Thanks everyone for all your kind words and wishes. To sum everything up in one post rather than quote and reply to everyone:
I said "no" to fixing the exhaust system and got a quote from 2 other places, both in the mid 1000s, which is still more than I want to pay considering how much I've put into my car already. I checked some accounts that some relatives had set aside for me and with taking a little out of my savings and maybe borrowing some money from my parents, will hopefully allow me to get a newer used car. I'm thinking a 10 year or under Toyota or Honda (I drive a '99 Camry right now), so if anybody has any thoughts or suggestions, please feel free to let me know.
My dog is doing okay, thankfully. The vet went inside and said what they found was sort of a free-floating neoplasm (a tumor that hasn't caused a lump). They removed it and are investigating it further, but they said it looks benign. To tell the truth, their diagnosis doesn't really mean anything because even now, my dog is energetic and happy again. Of course I'll still be anxious to hear what they say, but I would like to think that if my dog now responds better after having something taken out, that it's a sure sign that things are looking well for him. I'll be sure to keep anyone who's interested in the loop about what I hear.
And finally, the girl. Despite every urge of mine to to send a profanity-riddled reply back to her, detailing how much she hurt me and how I'd like to stuff her head into one of the waffle irons I'm sure she'll get as a wedding present, I politely wrote back that I wasn't interested in attending but thanked her for her invitation. I may come across as callous in my response, but to be honest, I feel that a cordial if somewhat icy response is even more than she deserves.
Again, I say "thank you" to everyone who took the time to post here, knowing that I have all your support really means a lot.