You're delving into an immature market. Off-the-shelf frame bags were basically non-existant 5 years ago; you had to get them custom made. There were a few people who did great work and charged commensurate prices. The industry has noticed, and you're starting to see low-volume runs of certain kinds of frame bags. The challenge will always be that different frames - even of a specific brand and model - are different sizes, and frame bags will need to be sized to match. In other words, the market will likely remain small and relatively expensive to enter as a consumer.
Enter the budget Sewing Machine.
$149 gets you an awesome machine that will do everything you need
(link).
If you can change your own oil, or fix a clogged drain, or basically turn a screwdriver you are more than competent enough to sew a custom frame bag that will fit your bike. There are countless tutorials on the web, and it really won't take you much time or money to craft up a basic bag that will work for some time.