Sonic Frontiers Phono 1: What's a NM one worth?

I saw one of these at a used shop the other day. It was priced at around $1,500 or so. Seems pretty high to me. On the other hand, they seem to be well regarded especially if they're sent in for an upgrade at Parts Connexion.
Too many variables to just list a price, condition, original box and manual, upgrades, tube type and age, etc. You could try searching the completed listings on Ebay, or buy a subscription to the Audiogon and/or Orion Blue books.

Looking at the completed listings on Ebay I saw that two of them sold in the last 3 months, for $691 and for $775. The one that sold for more was the Signature version, so yes, $1500 seems a bit steep.