Personally, I'd go with the average Bricklink price. Wall Price Guide, and Corner Wall Price Guide.
These are the price guides for an individual piece. If you are selling them individually, I'd go with the Average Bricklink price for each piece. If you're selling them as one lot, I'd add up how many you have, in this case 37 wall pieces and a corner wall piece, and add up the price for each individual piece, and add up the prices for a good lot price. In this case, it would be about $13.35 USD, give or take about a dollar. I'd go ahead and round it up to $15 USD. Then add however much you want for the baseplate.
I hope that this helped!