Hi and welcome to YT. So very sorry it's under these circumstances.
What is your girl's prognosis w/out the surgery but w/ the meds then...?
I used to work for Medtronic and was a pacemaker rep -- when we had "short-dated" (soon to expire for implantation into humans) pacemakers in our personal inventory - we would then donate them to the vet hospitals for implantation into dogs as there was still YEARS of battery life left on the devices. We would also then come into the hospitals once the devices were implanted to follow-up on the devices w/ our special computers...usually every 6-12 mths for the dogs.
Pacemaker surgery is not all that complicated, except for placing the leads correctly - which we would help the physician with during the surgery. But if your girl has a very enlarged heart...she could be at a different risk. What "testing" were they quoting $1000 for, bc that seems excessive to me...?
I'm not surprised that your previous vet didn't mention any heart issues bc 3rd degree block usually happens very suddenly.