The first 8 books in J. D. Robb's In Death series are on sale for $1.99 each at Amazon. Price matching doesn't appear to be in effect yet with other retailers.
There's over 40 books so far in this series, with no real signs of stopping. For the uninitiated, this is a police procedural romance series set about 50 years in the future with a stable long term couple. It's probably my favorite non UF or SciFi series.