Hi, I sell on e bay and use the cheaper option of one picture but i do add to gallery at extra cost. It seems to get more looks if you have a picture next to your listing.
I also add more pics in the add itself at no cost. If you upload your pics to a hosting site ( I use photobucket.com ) it cost nothing. Resize pics befor uploading, I use 400><300 , you can then use the html on e bay to add a link in your add to photobucket (tag). You can have a look at my add on e bay, it may give you a better idea ( no comments).Search (cabby-44) items for sale.
I hope this is of some help to you.
All the best