Find the suggested retail price by searching for an album's title on sites like Amazon.com or Overstock.com. The suggested retail price, also called the "list price," is a value set by the manufacturer. This is not a mandatory price for an album, but a recommendation from the people who published it. It can be a good indication of what price you should set on your own.
Look at how much the same album or similar albums are selling for on eBay. If you're attempting to price vinyl albums for sale on the used market, seeing what other people are paying for the same album can be incredibly useful. Of course, you can set whatever price you'd like, but if the demand doesn't meet that price, don't expect anyone to pay it.
Look at the prices at record stores. Most major cities and even small towns will have a few operational record stores in the area. Go inside and take a look at their prices. If a record store is consistently busy, that can be a good indication that its prices are fair and people are actually buying its products. That store's prices would be a good guide for the prices you should set.
Consider the price you paid for the album. Whatever your reason for selling the album, the end result is to make a return on your investment. If possible, don't sell it for any less than you originally paid for it.