Is it good or bad to include product price in page title? Page describes product, for example women's shoes. And price could be changed twice a year.
It shouldn't effect serp placement vs a descriptive word such as "price", "cost", "cheap" etc. as keywords.
Those types of keywords serve a specific search intent, namely transactional search intent.
Adding actual numbers would affect click-through rates, however for search engine placement price numbers would be negligible unless paired directly a qualifying transactional term.
i.e. "Cheap Widgets from 19.95", "Women's shoes under $20 - Free Shipping"
Search Engines can "do the math" on these terms and identify if the search intent is specifically regarding price.
Terms such as 'From', 'Under', 'Less Than' etc are a part of human natural search patterns which is clear if you observe Google Suggest for these terms.
This would be more relevant for manual quality review of search engine results (i.e. Bing HRS, Google Quality Rating System).
As pricing is less than 10 characters, I would classify it as "can't hurt" page title content but less value to pricing intent terms that I described above.
Because you're constantly changing the page-title, it might be better to keep the raw number outside of the page title and just lead from it in the Meta Description for consistency sake but search engines don't really care.
Unless you are specifically targeting the "shoes under $20" etc. search market aggressively, it might be more semantically meaningful to leave it out.
This depends entirely on your website, your (prospective) customers and lots of other factors prior to making the decision of having a changing price within the page title.