You have to look and see what New G17s and G19s are selling for locally, then start your 'asking' price at (about) 80% of that (if selling locally).

If after 2-3 weeks, you get 0 nibbles with your 80% price, consider dropping the asking price by $20, $40, or $50, until you reach a point where you either want to keep them, or use them as trade material.

If selling on the Web, Figure (maybe) 80% of what Web Stores are getting for New+Shipping+FFL Transfer Fees. Remember, if not selling Face-to-face, you (or the buyer) would need to add the cost of shipping to an FFL and transfer fees. The price needs to be pretty sweet for Online buyers to go through that.