If you're talking about drafts saved directly on eBay, you can save and store up to 5.
Edit: Hmm - it could actually be more than that - I went to double-check and had 5 displayed, but when I deleted one, an older saved draft appeared so that 5 were still displayed. If it does work like that, you wouldn't be able to access the older ones unless a new one was completed or deleted, though.
