Hi,
If you use fixed price, Buy-It-Now, you can set quantity to 50 and list for 30 days for 35 cents in US. The listing won't end until the quantity is exhausted or it expires at 30 days. The only qualification is feedback eligibility for fixed price and quantity at eBay.
If you have an eBay Store, you can also list the item as Store Inventory.
Note, Fixed Price and Store Inventory have higher Final Value Fees than Auctions.
Danno