Phra Ram Ratchaniwet Palace (พระราม ราชนิเวศน์), or simply Ban Puen Palace (วังบ้านปืน) is located in the southern part of town Phetchaburi within a military complex - but it is freely accessible, and at least according to the websites I have found it has no entrance fee.
The palace was built in European art deco style designed by the German architect Karl Doering. King Chulalongkorn (Rama V) ordered the construction shortly before his death in 1910, and it was finished in 1916. It was supposed to become his palace for the rainy season, and unlike nearby Khao Wang Palace the King chose an easier accessible location in the flat land.
Sadly we arrived there a bit too late - we did not know the opening times and the stay at Wat Mahathat took a bit long - so the palace was already closed when we came there. So we could only enjoy the view from the outside, and take several photos of the family posing in front of the building or the statue. But of course for the display here I have chosen only the photos without people.
A few photos from the inside I could find here, clearly worth to go again to see the inside as well next time.