If you act quickly and live in Canada, you might be able to score an MSI Pro Z690-A DDR4 motherboard from Newegg Canada, as they currently have the board listed for sale. This gives us an official price for the MSI board, which also gives us a rough indication of what to expect in terms of a price bump over the Z590 boards.
Newegg Canada has the board listed for C$279.99 (US$227), which should be compared to the MSI Z590-A Pro, which is listed at C$234.99, or a price premium of C$45 or US$37. Considering that the boards are almost identical in terms of features as per our earlier look at the leaked image of the board, bar an extra M.2 slot and an additional PCIe x16 slot, it seems like we can expect a fairly steep price hike across the board (no pun intended) when it comes to Z690 motherboards, as these physical connectors are worth the additional hike in price.
Update: It would appear that Newegg has realised their mistake and the board is no longer listed for sale.