[I wrote this around this time last year. It was just requested on a FB group. You may also be interested this chart “The Cost of Authenticity” from 2010.]
This is a question that comes up fairly regularly. Bonnets are expensive.
This is because they require multiple materials and require time to make them. 
To give you an idea, here are the materials that go into finished drawn bonnets and straw bonnets along with the price ranges for each item:
Straw Bonnets
- Straw plait ($20-$55 a skein depending on origin, plait and color)
- Millinery wire ($20/coil)
- Lining ($10-$15/yard)
- Facing ($10-$20/yard)
- Organza, net or lace for frill ($10-$30/yard)
- Bavolet net ($32/yard)
- Silk or Ribbon for Bavolet ($5/length to $30/length)
- Ribbon for functional ties ($2.80)
- Fashionable Ribbon ($4-$30/yard)
- Flowers ($10-$40)
- thread, sizing, etc
Drawn Bonnets
- Buckram ($4-$12/yard)
- Millinery Wire ($20/coil)
- Cane ($15 coil)
- Silk exterior fabric ($10-$30 yard)
- Lining ($10-$15/yard)
- Facing ($10-$20/yard)
- Organza, net or lace for frill ($10-$30/yard)
- Bavolet net ($32/yard)
- Ribbon for functional ties ($2.80)
- Fashionable Ribbon ($4-$30/yard)
- Flowers ($10-$40)
- thread, sizing, etc
To hand sew a straw form from straw plait, it takes between 6 and 10 hours depending on the type of plait and the shape of the bonnet or hat. Finishing and decorating varies.
If I Had My Own Blue Box: 
Thank you for the perspective on bonnet costs! However, the link that’s supposed to lead to a chart actually points to a post about an owl visitor, complete with pictures of a handsome owl.
Ooops. That is my other blog. Sorry about that. I’ll let people enjoy the owl tonight and fix it in the morning. Thank you.