And, of course, verify all this with their sites. I may have gotten stuff screwed up in my head, so any mistakes in this are entirely mine.
Authors' Billboard - $5 - they accept only .99, free, or new release titles. You fill out the form and pay before Tuesday and the ad will go in the newsletter for Friday of the following week. (I assume. I misread it last week and thought my ad would be in the newsletter following that Tuesday. Since it wasn't in Friday's newsletter, I'm guessing this coming Friday. If it's not there, I'll contact the newsletter owner.) You can submit an ad every thirty days per book. No data on this one yet. Seems legit. Newsletter looks good.
Update 1/5/16: The problem has been figured out. If you place an ad and pay the $5 thru Paypal, you have to click OK on the redirect message that warns you about sending data over an unsecured line or whatever. Once you do that, you get the confirmation email and the ad should show up on the date you selected. My ad should be live on 1/15/16. All is forgiven.
ReadCheaply - Free (for now) - they accept only .99 or free titles. Fill out the form and they'll let you know which date you'll be on. (Usually, I get first available within my chosen timeframe.) You get one ad every thirty days - regardless of titles. With this one, though, they only take blurbs of less than 300 characters (with spaces), so you might have to tighten that up a bit. I did this one back in October for Dying Embers' .99 countdown and saw no measurable jump in sales. I did this again last week for Wish in One Hand and saw a nice little jump. Newsletter looks good.
Updated 1/5/16: They're count of 30 days is off somewhere. I had an ad on 11/24. Tried to place another ad on 12/26 and their system wouldn't let me, saying I was within the 30 day timeframe. Then my KCD deals expired, so I'll have to wait until I have discount books again.
eBook Deals Daily - $5 for each target (i.e. $5 for Kindle, $5 for Nook, $5 for UK) - only accepts .99 or Free titles. I haven't tried this one yet, but I've got it on my to-do list. The newsletter, etc. looks fair. A lot of links, but not many covers.
Updated 1/5/16: Ran an ad through them for WIOH. Not sure if I saw any sales from it, but it looked nice.
Omnimystery News - pricing depends on what you want to do (a month long ad is $49, but there are free options, too) - not really caring what price your book is, but it needs to have a suspense, thriller, or mystery element. I've done cover reveals and book excerpts here (free) and those seem to do okay. I've also done the $49 thing and haven't seen much uptick. Newsletter is link heavy, but informative.
Goodkindles - $19.95 or less - doesn't really care about pricing, but obviously needs to be available for Kindle. For the $19.95 option, I got my book on their site permanently, a listing in their newsletter, and the option to bump my ad to the top after 30 days. Everything looks good. Not sure of the sales gain here.
Indie Author News - a lot of options so contact them for their rate sheet. I did this once, but I can't remember which option I chose. I think I ended up with a sidebar ad and didn't see any sales from it.
Every Writer's Resource - $10. Permanent. They say their ads are free, but then you have to wait for a spot and there's no guarantee. You pay them $10 and they pay attention. Professional looking full page for your book. Not sure what sales this has brought me, but the listing is there forever, so who knows.
Kboards - different options for different things (the link goes to their 'bargain book' promo page - $20) I did the 'book discovery' promotion ($15) twice. Once for Dying Embers back in February. Crickets. And again for Wish in One Hand. Again with the crickets. But I have heard Kboards can be an amazing place to advertise. Not sure why my experiences haven't been amazing. Maybe you need to be active on the Kboards forum. Maybe it's not the target market for my books. :shrug:
Ereader News Today - check out their rate sheet. It's dependent on your genre and the cost of your book. The books have to be discounted in some way, and they're more favorable to free or .99 books. I did a Suspense ad for Dying Embers and a Mystery ad for Accidental Death. Both gained me upwards of 100 sales each, so it was worth the cost. However, ENT is extremely picky about who gets to advertise with them, and it's not always clear exactly what they want. Dying Embers had more reviews when they accepted the ad than Accidental Death, but AD only had 3 reviews when they accepted it. However, I can't beg an ad for Wish in One Hand, which has 5 Amazon reviews. Even after I changed the cover. So who knows?
There are, of course, way more places to advertise and their pricing varies widely. If you know of any inexpensive advertising venues, help a fellow indie out and leave a link. And if I discover any others or find more information about any of the above, I'll let you know.