I am guessing you prices are based off the amount of time it takes to walk and collect shells and the time to create the piece. Maybe in your listing, include some information about how you collect shells and the time it takes, and talk a bit about the construction method. I feel like when someone understands the time and energy it takes to create your product, they are more willing to pay the price for it. Personally, from looking at the product, I would pay around $45 for it.
Maybe include a photo of how it is packaged, or a close up of detail to add more to the listing. The shipping price looks good, as I am sure they are quite heavy, though I like to use the flat rate shipping boxes for heavy stuff so it is also shipped quickly. Good luck! :)