go to pcpartpicker.com ... Select Individual Parts, and then select Motherboards.
On the left side is a series of filters. Check the Z170 filter, and set the price ranged you are willing to pay. On the price ranges, it is much easier to click on the actual numbers and type them in manually, rather than sliding the dots back and forth. Make sure you make the low end at least $1 to eliminate the motherboards that show up without a price since they are no longer available anywhere.
Once you have that done, scroll to the far right side, and up. Click on the Price header until you get the lowest priced boards At the top. Pay attention to the ratings column. Anything below 4 stars means you do not want that board.
When you find something that interests you, search for some reviews on that board, and see what they like and dislike about the board.