Is the new construction in a development? Or, was an older dwelling razed with a new dwelling built?
Whichever the case, with such limited data, I would do a market analysis on the subject's immediate neighborhood including recent sale prices of "the most similar" properties in size, bed & bath count & lot size in the area. Then, another analysis of the market area including all the sales within the last 12 months and base you overall market trend off that.
Of course explaining the lack of new builds within the immediate and alternative, competitive neighborhoods. That's about the best you can do..... no one else is going to magically find what you didn't.
If the subject is in a PUD, go to the sales office and get a printout of the last year of sales (if they'll give it to you) and do an analysis of those (list price, sales price, DOM, etc.)
Good luck!