ETA: #2, I reposted my ad on craigslist after d-bag#1 cancelled and had another buyer respond within minutes, came and looked at it, and left a deposit on the spot. He'll be back with the other half to pick it up within the hour. I guess I should be a little more patient lol. But, with cash in hand, I called the vet and scheduled her. So Monday morning she'll go in for treatment!
ETA: So, the guy called me today, 30 minutes before he was supposed to pick up our old Jeep, and told me that he decided against it and wouldn't be coming for it. Now I'm back to square one. This was a little crushing. I've been on pins and needles all day hoping I wouldn't get that call, hoping that he would show up as planned. Kinda bummed right now. 
There has to be a science behind Knottie Vibes, because someone bought our old Jeep for $400 and a very kind receptionist at a vet clinic I spoke to must have pulled some strings or something and gave me a quote of $501 (for the WHOLE treatment process) after speaking to the vet specifically about my situation. So, even though I didn't get the whole amount together, she says I don't have to pay all up front, maybe only about 60% or so to get it started! I'm so happy!
We're still not out of the woods yet as the treatment itself is literally an injection of arsenic and dangerous, so she has a ways to go, but at least we're getting it started. So, as a message to anyone who thinks that the prevention meds aren't worth the expense, as minor as it is, it's INCREDIBLY important to keep your dogs (and CATS too! There's NO treatment for heartworms in cats!) on prevention, even if mosquitos aren't prevalent in your area. Even though there is a treatment for the condition, it's painful and hard for the patient.
She will have to be on antibiotics after the medication is injected. She will be kept almost sedentery for the whole 2 months of the treatment because the heartworms will be breaking up and dying within her body and she has to be calm for her body to dispose of them. It's a hard process and an incredibly difficult lesson for me to as a pet parent.
I still want to say thank you to all of my September girls for the kind words and positive vibes! It's not over yet, but a positive start is always a plus!