If they are bought at a legit chain pharmacy they are not cost effective. Last time I ran these they were almost 17 dollars per 1ml amp, expensive but real pharma.
We do have a cool little black market here in the city. It covers about 2 square blocks and there are just a bunch of guys standing around and they run up to your car and ask what you are looking for. If they have it and you agree on price then they duck into a house or little business and bring your stuff out.
There stuff seems to be legit and less expensive than the real pharmacies, so if you didnt pay around that price per amp, then it had to come from a place similar to that.