We stayed at both, Ventana Inn and Post Ranch Inn, several times. If you want, click on my name and there should be reviews around 2006-2010.
Ventana sort of lost its soul after it was purchased by a corporate entity. Rooms were extensively remodeled after the aquisition and after the fires in Big Sur, but service was impersonal and the food in the restaurant was a far cry from what we remembered from our former stays.
Post Ranch Inn is magnificent in so many ways: incredible setting, private, attentive service from everyone on the property, great amenities: spa, Shaman session, views all around, infinity pool in a dream setting, library, stargazing, incredible breakfast (included) and wonderful food in their restaurant.. I could go on and on.
Post Ranch is more expensive but rightfully so and it is worth every dime. I doubt very much that you would drive away feeling that you overpaid or that it was not worth it. You could go to Vegas for a weekend and by the time you paid for a decent hotel room, food, spa, saw a show, and gambled some, it would be more then a weekend at Post Ranch Inn, and you would not get to bond with your partner.
Here is what I would recommend.. Do not get too fixated on the ocean view room. IMO, you would love any room. Take a look at treehouses, which are uber romantic and are around $700-$800. Some of them have at least partial water views. Perhaps a room in the old Mountain View House or a lower level Coast House. The amenities are the same no matter which room you stay in and in July you would likely spend lots of time outdoors. So, just sit on one of the benches overlooking the ocean.
Call the Inn and speak with one of the reps there. Tell them that it is your special Anniversary but that you do not have unlimited funds right now ..;)
Edited: 10:42 pm, January 19, 2013