I don't know if I have a
strong recommendation, but I still enjoy the collaborations (including the NUMA Files series and Oregon Files series) well enough. The main thing I don't like about the later Dirk Pitt books is the trend towards the character's kids as the focus rather than Dirk Pitt, Al Giordino, etc., but alas, heroes must age eventually, I suppose.
Price is down to $16.02 now. It'll probably still be another week to 10 days before it's $9.99 if it follows recent/usual trends.