He's fishing as Firko said. $5000 tops and that's too much.
The only Frontera worth anything like that IMO is the Ignacio Chivite Frontera that he ran without success in the Dakar 2011, and 2012.
At least it had a bit of history along with Yammy forks etc.
I see Ginger Molloy is trying to sell his TSS for $40K again, good luck to him as well.