I used to (like, 5 years ago) find a lot of $7 and $8 bombers that were pretty great, or $9 6-packs that were damn solid.
From my perspective it's not so much that I stopped buying mid-tier beer, as that it vanished and isn't there to buy anymore. Now I look at a $12 4-pack of beer that's not even that good and wonder if I should put the money toward a very-nice scotch instead....
I still buy from a few brands that I know well and that do deliver good quality at non-crazy prices, but there just aren't as many "yeah, sure, at that price I'll give it a shot" beers on the shelf. At least locally.