I just noticed the old link to the form doesn't work anymore. My guess is the update to new version of google Sheets might have broken it. That might explain the drop in contributions too because users couldn't access it?
Have recreated the form, here are the new links to use:
To contribute a price update:
http://bit.ly/1MRkaDb
To view the price updates:
http://bit.ly/1IpmVvF
Note that there are two sheets within the document now. Clicking on the above link will bring you to the sheet that will collate the new responses. Click on the "Updates (Archived)" tab to view the previous set of responses. Google sheets has a limitation where they don't allow you to send new form responses to an existing sheet, only as a new sheet.
Google also removed the List View in the new version of Sheets, so Menu > View > List doesn't work anymore.