Hi,
If its the same 400 products prices to be updated regularly, i would suggest to have a custom plugin which will allow you to download a CSV(Excel) file, which you can edit locally and then update/import back to wordpress.
I am confident to deliver more than your expectation, if given a chance.
Kindly have a look into my profile, checkout my completion rate(100%), and what other clients say about me in reviews. If it interests you, lets discuss more of the project.
Thanks and Cheers.