I’d recomend having a look at the better records website. I’m not advising paying those prices, but there is a wealth of knowledge to be gained on what classical pressings sound good and some history behind the recordings. I’ve bought numerous records from there over the years. He, Tom, generally sells the quietest most dynamic pressings of classical recordings. He’s already listened to the records with his team to guarantee this. Also offers money back if not happy. He sometimes reduces the costs on some of the classical stuff, so you can often pay less than 100 for a known quiet and good sounding pressing.
I’ve also gone the ebay/discogs route and have had descent success. Also, thrift stores sometimes have some great classical records, but the lighting is typically not very good, so you must be careful and look closely.