Discus shouldn't be 45 pounds each, either the fish shop is overpricing or they are high quality sub/adults.
It's best to buy of a local breeder, theres always one close if you look around enough...They should know what they're doing, unlike most pet shops which don't, and their prices will be much cheaper.I wouldn't pay any more than 25 pounds for a standerdish (made up word

) discus when young, and adults maybe 50 pounds max, and only if they're good looking and at least 6 inches...Picking out what discus you get is crucial, I'm seeing so many bad strains and stunted discus.
Another plus point with the breeders is you get to see their fish, which is not just fun but also gives you an idea of what their offspring is going to look like.
Discus aren't just expensive to buy, they're expensive to keep...If you waters not ideal you should invest in an RO (reverse osmosis) unit, which isn't that cheap nor efficient but does the job.The top quality flake, granules and frozen food isn't cheap either, and they should be fed at least 3 times a day, and thats for fully grown adults.Fry should be fed at 8x a day...I would buy sub adults/adults (around 4-9 inches) as its hard work carrying out daily, maybe every second day, water changes for quite young discus (4 inches or less) and then you have to keep up with feeding, making sure you feed exactly the right amount.
Run your tank for a couple of months and get all water params perfect, pH, ammonia, nitrite and nitrate are the main.pH should beanywhere between 6-7.6, and maybe even lower for wilds.You can lower pH with bogwood and peat...Keep doing researching.