Two books in the Jack Colby, Car Detective series are $0.75 each right now in the US, which is a pretty good price, since most e-books don’t usually go below $0.99. (Unless they go free, of course…) Sadly, the sale is only at Kindle US, not at Kobo US…
Buy Classic Mistake, #4 at Kindle US
Buy Classic in the Dock, #7 at Kindle US