WCCF Tech reports Intel's Z490 is expected to be announced in May. The actual availability date is unknown, it could be May or earlier/later. These motherboards are required for the Comet Lake-S processors, which use the new LGA1200 socket.
The site heard from a motherboard maker that the Z490 boards will be about 3 percent more expensive than their predecessors:
So we have just heard from one of Intel's AIBs that the company is preparing to announce its Z490 motherboards sometime in May. To be clear, this might not mean that you will be able to get your hands on them in May, just that they will be announced during this time. Intel's Z490 motherboards are going to feature improved VRM solutions and will be very slightly more expensive than their predecessors (think around 3%).