In a free market cocain and heroin should cost about the same as OTC generic drugs. That means your 1000 usd/day heroin habit is now a lot less than a coffee run to starbucks.
Looking at the official NHS pricelist for May 2015, 100 10mg Diamorphine (Heroin) tablets cost GBP 24.09 which is a lot cheaper than street prices...
I'm guessing a GBP 80 (1/16 oz) per day habit could drop to around GBP 10-15 (not really sure about purity, but assuming adulterated to 10% would mean 0.1g street Heroin is equivalent to one of these pills, so that would be the equivalent of 10g or over 1/4 oz which would be GBP 160 probably)
There is widely considered to be a shortage of opiates for medical services around the world, and this is in part due to the very, very strict controls on growth and distribution of the product. This is in part why the cost is as high as you say there.
We seem to be getting a lot of stuff wrong in this area....
I'm guessing a GBP 80 (1/16 oz) per day habit could drop to around GBP 10-15 (not really sure about purity, but assuming adulterated to 10% would mean 0.1g street Heroin is equivalent to one of these pills, so that would be the equivalent of 10g or over 1/4 oz which would be GBP 160 probably)