You should be able to do this in bulk by first using the "Find & Replace" feature for your Saved Listings (to change their format from Auction to Fixed Price,) then
use the Bulk Edit to make sure they have the correct prices. This process may look long, but it really isn't too bad (a lot quicker than changing them all individually! lol)
Go to your Saved Listings page and check the box next to the Saved Listings you want to change from Auction to Fixed Price. I find it easier to do smaller batches of listings at one time (less than 100), otherwise it can take too long and time-out.
Click on the Find & Replace button (next to the Bulk Edit button.)
On the next page, where is says Field, select Sale Type from the drop-down menu.
Then you will see "Find Sale Type" (which is where you would choose "Auction")
And then the "Replace with" (where you would choose "Fixed Price"
(Note that when you are switching from Auction to Fixed Price, the original starting price of the auction will become the new "Fixed Price" by default. Don't worry-you can correct them by using the Bulk Edit, as noted below.)
Confirm the changes on the next page and click the "Confirm Selected Listings" button.
To adjust the new Fixed Price (if needed), re-select those listings and then you can use the Bulk Edit feature to update them all at once.
Let me know if that works for you or if you have any questions about how to do it