On Flippa you can list as either an auction or a classified. More information about the nature of the different types of listings can be found here
The Flippa listing fee (see here: https://flippa.com/#pricing) covers all listings for a 3 month period. This can be for a single listing or for multiple re-lists of that original listing within the 3 month period (starting from the date at which the listing is purchased) if the original listing is closed or cancelled.
Please note that whilst classifieds are open-ended (no specific end date), auctions have a default period of 14 days and must have a duration between 3 and 30 days. This means that if you run an auction that ends unsold within the 3 month period of your listing fee, you can re-list that asset for free during the remaining 30 days up until the end of the 3 month period. Re-lists outside of the 3x month period are at 1/2 price.