I have several years of experience in marketing and optimization in the eCommerce space for one of the largest online jewelry retailers in the U.S. I also have several year of experience working with online retailers that operate under a subscription models.
In order to answer your question, you will need to consider the following:
Will your subscription revenue generate enough income to maintain the operational strains of this business model and be profitable?
If you do not know the answer to this, you need to work backwards to arrive at the monthly pricing for your subscription service.
Some things to consider:
1. Cost associated with operational logistics like shipping and fulfillment (assuming customers have to receive and ship the jewelry back to you)
2. Carrying costs associated with holding on to inventory on consignment. (assuming you will not own the jewelry outright) This may come with other contingencies like having to carry insurance and the operational aspects that will help you handle recovery of lost / unreturned inventory, etc.
3. Costs associated with building a transactional platform that is built for the monthly activity you will have with a subscriptions service. If you take Macy's for example, most customers place online orders 4 times per year or so. In your case, the nature of your model requires a different platform as you will be taking recurring payments, arranging returns, maintaining credit card / payment information, etc. In short, its a different animal that your startup eCommerce type platform.
If you'd like to get more details or insights I'd be happy to hop on a call and chat.