Hi Jason,
I am a full stack web developer with more than 12 years of experience. I agree with people who said "clone of ebay is costly". Fortunately, we have options. There are many shopping cart software that are available ranging from free to any value you can imagine.
If we use any available software, we save time & money building it from scratch. Also we get upgrades from the vendors. Only cost we will have upfront is the cost for customization and later maintenance.
If you are interested, I can help you chose a solution and build a solution around that. Please convey the details like what you are going to sell, targeted audience etc for better suggestion.
Looking forward to grow together,
regards
Varghese Chacko