These fintail wagons are rare and fetch quite some money, even in bad shape. I would not be surprised if it got over $1500 if posted on eBay. But it's always good if you can get it for less than that.

You should seriously consider grafting all the specific wagon panels onto a solid W110 or 111. It will be cheaper, faster and the end result may be better. You should consider keeping the sedan you have for that, unless it is also rusted. Otherwise there was a guy wanting to get rid of a sound W110 a few days back in the Bay area. Engine not running and car had been hit in the back and repaired earlier in its life. His wife was putting pressure so that he donates it, so you could have a good deal if he still has it: http://www.benzworld.org/forums/vintage-mercedes-benz/1565265-help-home-needed-1967-230-a.html