Hi, you need to have eCommerce platform for your website which can connect to your eBay store and synchronize the products on both end. I've done it for few customers and have created eCommerce website & eBay store and got synced so, if it sells on either end it update inventory.
There are many more features you can use from your website.
But, I'm sorry to tell that you budget is too low to have such platform of selling. If you're going it sell online you need to have present on good eCommerce website and Amazon, eBay, Rakuten's like marketplaces.
Let me know what you think so we can talk further.
Thanks,
Skpye= zestkhan