I'll try to give you some real help on pricing.
When I look at pricing, I basically figure out where else I can buy the wine and at how much to determine value. But, on top of that provenance is a big deal when it comes to expensive bottles, especially older bottles like your 74 Martha's.
There's a load of retailers offering it for $799 and it'd be likey that I could call them up and get the price down.
The last bottle at auction sold for $479 in May at Bonhams and Butterfield.
So, if I were interested as a buyer, I'd first ask you where you got it and how it has been stored. Of course, if you have a reputation for maintaining a well kept cellar that helps too. But, it takes time to build that reputation.
I bet you may have received emails asking these questions already.
As far as winecommune, I wouldn't use them to price. As far as selling throuh them, I think you have to pay them a % now (was different in the old days). You might check it out.
I don't use winezap often. But another new thng on the market is vinfolio. They'll list wines that they have sold and the dates/prices. If the bottle has actually sold, that's an idication that yours could too at the same or near the same price. But again, provennce could swing prices of the expensive bottles quite a bit. A quick glance, but I don;t see any sales of 74 Heitz on VF.
Depending on bottle condition / provenance, I might be interested in your 74 Marthas. Can you either post provenance info here or send it to me via email? email@example.com