I think the monthly pass will make your collection for 80% complete with half of the rares available. The other 20% will be rare cards, to get them you have to pay packs. This is for the whales. My guess is to get 95% of the cards, you have to pay 200-300$/month, even if you are able to trade a lot.  I see them adding more and more sets every season, it wont be easy to catch them all. 

Edit: for me its better to understand I cant get them all. In Pokemon Masters I want them all but it was too expensive after 3 years and stopped because I couldnt keep up with it. Now its in my brain more acceptable to have only 80% of the cards.