I am an active Udemy user for a long time and what I have noticed is that they're ALWAYS having some kind of promotions (e.g. courses for $9.99/$10.99/$14.99), so please do not ever purchase the course at full price. However, individual instructors can decide if they want that these massive promotions would be applied to their courses or no and they can set their own prices for their courses. Therefore, it happened to me that the courses I wanted to purchase were not discounted despite the fact that Udemy was running massive promotion on their site.
In this case, individual instructors can generate their own coupon codes and run promotions individually, so one of the tactics is to contact the instructor and try to get the discount. Another option is to look through some coupon code websites. You should not expect much from them as most of the coupon codes are rarely updated, but these are several ones with which I had good experience:
- groupon.com/coupons/stores/udemy.com
- bitdegree.org/udemy-coupon-code
- udemycoupon.discountsglobal.com
I often use these websites to look for Udemy coupons.
Now, regarding the quality of the courses, I agree that (especially these days) it's really hard to determine a quality course because there are just so many courses uploaded on Udemy. People have noticed that you can earn easy money by selling your courses and started to focus on quantity rather than quality... However, when selecting some Udemy course it's good to look over the reviews. I understand that they can also be 'fake' and not genuine, but it will help to get an overall view. Also, the enrollment number can help to determine whether the course is worth the time or no.
I'm not an expert or anything but there are just some of my notices from using Udemy for about 3+ years now.