You should never regret missing out on a poster for being cheap, because you will always get another chance to buy what you want for the price that you want.
LOL
80s - 2010s - absolutely true, and probably next week. (it's just Back to the Future, don't panic)
60s - 70s - probably true, might have to wait a month or two (it's just Breakfast at Tiffany's, don't panic, next HA catalog will be here soon)
50s - hopefully you can find one within the next year (but not if you are waiting on a 50ft Woman 3-sheet or something)
40s - yes, you might get another chance before we elect a new President (unless it's a Wolf Man insert)
30s - you might get another chance, when that buyer dies (I passed on the Mummy 1-sheet, cause T said another will come up for the price I want)
20s or earlier - good luck with that. (I'm sure another Metropolis 3-sheet is around the corner lol)
And if you don't, buy something else. A lot of dealers abuse the hobby and it's a shame. Patience is key.
As long as you are willing to settle for something that wasn't your first choice, there will be lots of things to buy.
Dealers abusing the hobby sucks.