You could try contacting either a record collector or auctioneer, who are experts in this field. One way to do this is to search the yellow pages in your area. Yellow pages can also be searched online.
If you wish to offer your record for sale you may also like to contact the National Film and Sound Archive. However, please note, the National Film and Sound Archive does not offer a valuation service.
Links to record collectors and auctioneers in Australia and overseas can be found on the Books & Collectables website.
There are print items available, which can help you to price your record. To locate library holdings of these search Trove. Try the search terms “sound recordings prices” and/or “sound recordings collectors and collecting”.