Question Price Comparison Tool - Automated

Hi,

I'm looking for a tool which automatically detects big price differences between websites, such as ebay/amazon/etsy/aliexpress for dropshipping purposes.

I know about Profit Spy, but I am not willing to pay 70$ as I have no products up yet and all I need the tool for is product research, not the other features.

Any suggestions for a free or cheap tool (<20$) is appreciated