For me it was probably Thrice's Alchemy Index. I paid around $130 for it and I don't think I can afford to make any more record purchases like that again lol
I have a small collection around 100 records. I think my most expensive was an earlyish pressing of Eric Clapton Unplugged double disc for around $60.
I almost got a copy of The Everglow by Mae for around $300, but thankfully they decided to do another short run and I picked it up for about $30 or thereabouts. Sounds great, too!