Hello,
We propose to custom code the website using Symfony 2 which is inspired by Django's architecture. It is an MVC framework based on PHP and is extremely scalable. However, if you are still willing to go ahead with ROR, we could do that too.
I have seen the Etsy clone script from Agriya and I see that it has most of the the features you have requested, but not all. For instance,it does not have the option of choosing cutom product templates. Although it has an option of multi-store, it does not allow you to customize the store template like eBay. Also, the etsy clone script does not seem to have an ad management platform. But on the brighter side, it does have most of teh crucial features such as adaptive payments, internal messaging etc.
So even if you use an off the shelf solution (agriya or anything else), we will still need to custom code a lot of things. However it would be cheaper than scratch development.
To give you an idea....
For a complete custom development of all features and modules, the cost would be around $ 5000 to $ 5500at a timeline of 60 to 70 business days with testing. However if you use an off the shelf script and we add in the missing modules or customize the existing modules, the cost would be around $3200 at a timeline of 40 to 45 business days with testing.
Therefore what I suggest is this.....
If you wish to go with agriya script, please go through the demo and let us know regarding the customization you with to implement.
Thanks,
Pra