We usually buy games via Amazon or the local game store. Some games we pay full retail price, some games we don't, because the savings is significant or we want to buy local (the game shop guy gives great recommendations, so we like to patronize his store). I've purchased many via the Amazon "used" or "buy new" links, and also have purchased games via eBay.
One factor I'm not sure that was mentioned was re-playability. Some games just have that factor of being able to be played in multiple ways, so you want to keep replaying it, as the strategy changes each time (or somewhat changes). I am not familiar with most of the games on your list, but one game I'd highly recommend is the Dominion Big Box--it has so many options for playing again because the cards you play with can change with every game (and if it's just you and the wife, it also works well as a two player game). I just gave this to my husband for his birthday in December, and it's been great--it's also very easy to teach new players, so the bar is pretty low as far as getting a third or fourth player involved.
Also like the ideas of game swapping, or sharing your list with friends who also collect games, then getting together for game nights. We do this with my family (different family members own different games) and it works very well. And you may discover you don't really enjoy a game as much as you'd thought, or that you absolutely must own your own copy of something (for example, one play of Lords of Waterdeep and I wanted to own it, but I've played Flapjacks & Sasquatches many times and have no desire to own--happy to play with the friends that own it, though).
Edited to add: the supposed high cost of games is totally worth it to me. A lot of time goes into good game development/design. I recently paid for two games via Kickstarter to see them made, and will do anything I can to help these projects along--one is Wizard School by Hank Green, the other is Secret Hitler by one of the guys from Cards Against Humanity. Designing a great game is tough work, and not very lucrative. I'm happy to pay the price of games to have game designers keep making them.