Generally they are referred to as a singular if the keyword comes after it so in this case low xx,xxx MAYBE, more likely $x,xxx because of hype from sale of other actual singular name...this is similar to owning leatherswallet.com or checkingsaccount.com and so on..
Honestly it might be better to hold onto it for now and see if traffic grows or what the guy does with the other one first.. In the long-term you might derive more ppc from it then selling it if it actually gets any traffic which is possible but that is another MAYBE
