The 88-123lbs is $5.00 cheaper from Chewy, if you set it up on auto-ship you'll save another two dollars. My vet is trying to get me to switch to something they call Trio with heartworm, flea and something else in one dose. I obviously need to do a bit more research.
I now use the trivecatrio (sp?), it’s only $35/month from my vet. It’s for fleas, heart worm and parasitic worms. I will never again go without heart worm medicine as my boy I just got heart worm and the medicine to get rid of it runs $1200. And they must be kept calm for 3 months during treatment. It totally sucks!