Several things:
First, I hope it is not free!
Second, I hope you have a grabby title. Thirdly, I hope you have a grabby title, and fourth, I hope you have a grabby title.
Have you investigated the Amazon connection on this? They may take 35% (I think) but the remaining 65% on hundreds of thousands of copies could be a serious wad in your pocket.
Do you have a blog? Be an only slightly obnoxious blogpimp.
If you have no blog and no intent to create/maintain one (it IS work) then comment on other peoples’ topic-similar blogs and if you are too shy to promote your item directly, then try to incorporate phrases particularly if the appear in your title. You sell 25K ebooks for $3 (cup of coffee = a no think transaction) and Amazon takes a buck, you could make $50K. Yes you could. it is a FABULOUS business if you can get it going and they do all the work for you.
Above all...spend some time on the title! The title could be wroth several tens of thousands of dollars to you.
And start writing your next one!
You could also try Clickbank which lists and sells digital products. Basically, you list your ebook and other people can sell it on the net through various techniques such as blogs, websites, Facebook, etc. You’re probably going to want a webstie with a sales page for the book as well.
The most successful people on clickbank have some sort of joint venture going with other publishers however. So, you may want to explore those options first and then launch it on clickbank.
Go to fiverr and google amazon reviews...I believe you can still buy them there as well if you want to add a few reviews as well. There is also a fiverr gig where you can pay someone to promote your book.
Setup google alerts for your keywords and post about the free download to as many sites as possible.