I somewhat arbitrarily set myself a limit of $100 for any and all LP’s, breaking that rule for only one title: the MoFi 1-Step of Tapestry. I care enough about the album to pay for the first really good (in relative terms: Lou Adler was not a record producer who made audiophile quality recordings. The recording itself has always suffered from mediocre SQ, particularly of the piano and voice) version of the album.
I recently found a stone-Mint copy of Church Street Blues by Tony Rice, for which I paid $80. This great Bluegrass album on Sugar Hill Records features excellent SQ.
The best LP investment I ever made was getting the Beatles In Mono boxset while it was still in print. I paid whatever it was going for then ($250-$300), and it now changes hands for many multiples of that amount. I then sold all my MoFi stereo Beatles LP’s, keeping the original stereo Parlophone pressings I bought back in the late-60’s.