ttcParse.py provides a way to download pricing data from Tamriel Trade Center and use it to autofill most prices. Simply go to your TTC addon folder or download this zip and copy the PriceTable.lua and ItemLookUpTable_EN.lua into this directory. Run the ttcParse.py Python 3 file, and a prices.json file will be produced.
Included in this git repository is a precompiled prices.json which you can also use, but it may be a bit out of date.
Finally, take this prices.json file, and under the Price Import/Export box on the website, select the file then press import. Prices should be automatically updated.