Just priced up 18 24 vac coil relays and bases at about A$ 130 to A$150.
Would the attached sketch work ?? It would cost only a few diodes and caps.
The DC output would be fine cause most of my existing solenoids are DC.
Tested it on LC Spice and it seems OK but I really know nothing about this stuff so would appreciate a comment from someone more knowledgeable than myself.