Hello,
I’m really sorry it has happened to you. The only way I can think of such problem to occur is if you have two admin users accessing our “Bulk edit costs” page at the same time, and the second user clicks on the save button after the first user has saved. Excluding that possibility, I wouldn’t know what might have occurred.
Unfortunately, if you didn’t have a backup it won’t be possible to recover your data.
Apart from that, we are saving the costs in a post meta key called _alg_wc_cog_cost
. You could try to export your products and take a look if the costs are there but located in some other column for some reason. If that’s true it will be possible to run our import tool to the correct meta. I can try to help you with that if you wish.