I want to keep track of product prices on a series of websites, perhaps using a simple workflow like this:
Separately, another macro periodically checks all these previously saved records, and alerts when a price has decreased.
Does anyone have any clever ideas?
There are a lot of issues with doing this. Firstly, do you have a Mac that you can permanently dedicate to this task, or do you want it to somehow operate in the background without opening a browser to read the data? This is one of the biggest questions you have to answer. Background processing is possible, but it forces a certain kind of solution that may not be the easiest.
The next big decision is whether you can (or cannot) identify the items that you want to track and have the solution track only those specific items, or do you really want a macro that can detect the item on a generic page and find its price all through the mouse selection method you described above. That is a far bigger can of worms that you can imagine. The best thing to do is start by monitoring a single price on a single page and then maybe work upwards from there.
The next question is how do you want to be alerted. Do you want an iMessage sent to your iPhone? This is the easiest part of the problem.
The next question is how does the programmer of this macro extract the data if you haven't shown us the URL or the HTML code that the page is on? I'm guessing that you're getting this data from a paid website that we don't have free access to. If so, have you checked into whether they provide a notification service already? I would think that they might do this for you for their included fee.
Another important thing to understand is what you mean by "when a price has decreased." Do you mean any decrease at all, or are we talking about hitting certain thresholds?
I'm always willing to help solve problems, but we need to start smaller than "I want to highlight an item on any web page and let the macro track the price and notify me of changes" which is probably way to broad a problem. You should start with a narrower problem.
I hope I'm not sounding negative. I'm doing my best to help clarify what the issues are.