I was always told that heartworm treatment was very expensive. We had a dog long ago that went thru it. We rescued our old cocker, Toby, from my son and his, at the time growing family. They didnt treat him as they should have. He had heartworms for a long time.
We were told by a nice vet just to keep him on a little stronger dose of meds and he would be OK. That was about 7 yrs. ago. He is now nearing 13. Even with a congenital heart defect, they didnt get him down. I cant keep him out of the pond for a swim, when we go down to it.
Dont let the heartworm be an issue.

Also recently adopted 2 juvenile choc labs. They aare the sweetest animals there is...they think they weigh about 3 lbs.