When you delete a project, all bids within that project are deleted also. You see the project and the bids in the Recycle Bin, but you cannot restore just a bid from that project - you must restore the project which restores all the bids. However...
Restoring a project only restores the project to how it existed when it was deleted. For example, if you delete all the bids in a project, then delete the project itself, you see the project and all the bids in the Recycle Bin, just as you would if you had deleted the project without deleting the bids first. Now, if you restore the project first, that puts the project back but none of the bids are restored, because they were deleted before the project.
Deleting Projects and Bids