The best "price guide" is eBay; it's a national market - mostly the "Completed" and "Sold" listings, but the "For Sale" listings too, as this can be a hint as to sellers' current hopes, dreams and expectations - which can inform your expectations, too.
It's the only place I go when I wonder what something is or is not bringing currently and recently.
If you live in an area with bunches of train shows, that can be a real indicator, too, at least in your region. Most in the US don't live in that world.
