I think it was rare a few years back, but after it got issued as a greatest hits game, the price plummeted - same for FFTactics, same for Xenogears.
My Xenogears second-hand greatest-hits version also became mine for about 20$.
As for Lunar 2: Eternal Blue, I cannot find it in any stores in my area () so I cannot say what the average price is. It is a rare game (off of eBay, anyway).