Vet my idea - price comparison & alerting

I’m building a price comparison and alerting site for a particular vertical of consumer good. There are a lot of retailers that sell in this space (Amazon, Walmart, Target, and many boutique sites), and prices for the goods are volatile (frequent sales). So the idea is to collect the prices from all the retailers in a single place for searching and also enable email alerts when a product’s price drops below a user defined amount.

Because of the price alerting functionality, I don’t think I’ll be permitted to leverage affiliate links (not Amazon’s, at least) to generate revenue (Amazon’s ToS requires special approval for this type of functionality).

So I’m planning my main revenue source to be a monthly subscription fee that would unlock more features (unlimited price alerts, etc). Non subscribers would be served ads for some revenue as well.

Implementation-wise, I plan to collect all pricing data via web scraping (because either I won’t be able to be an affiliate or because the boutique retailers don’t offer APIs anyway).

Are there legal concerns with this idea?

Nothing I’ll scrape is behind a login - it’s all publicly available data. But I don’t see examples of other sites doing this sort of thing (there are plenty of affiliate sites, but I don’t see them doing serious price comparison functionality across many retailers or price alerting), so I’m wondering if it’s because I’m going to get a cease and desist or because this is just a bad business model.