Dog meds

I had my (large) dog in for an annual check, and got Nexguard spectra for heart worm/ticks and was shocked that it was $250 for 6 pills. I paid it but looking after realized the same thing seems to be available online for $106 from a Canadian source. I'm wondering if anyone can comment on buying pet meds online.

I don't recall the prices being that outrageous before, but there has been a change of ownership at our vet.