Finding the best deals and prices on the Internet is definitely not easy and you have to visit multiple websites to compare prices between them and find the lowest price for buying a product.
FoxyPrices is a handy extension that shows you non-intrusive alerts while browsing for products, the alerts shown do not contain any spyware or adware links as well as do not link to affiliates.
Using it for sometime I was unable to find any price changes, which would mean that it does not hold a very large database for pricing comparisons, but reading the comments I could definitely say that it worked.
The add-on is experimental, so you will require to create a account before you can download the extension. If you do not have a account yet, feel free to use the credentials from below.