Each camera obscura offers unique challenges and the costs must be matched to the customer’s resources. I’ve noted below some of the factors in my rough estimates.
The most valuable single item in the budget is the lens. The diameter of the lens depends on both the distance from the lens to the table and the importance of having a bright image. You may be forced to select a lens of longer focal length based on the constraints of an existing building. For a given aperture, a longer focal length means a less bright image. Doubling the focal length gives an image only 1/4 as bright.
If you desire a motorized system to focus the main lens, tilt the flat mirror up and down, and open/close an exterior door (or to vary the speed of any of these operations) be aware that these features will add to the total cost.
Some users are artists who can exploit a lens without a flat mirror to produce a light and color show. Such lenses might cost from $3000 to $5000 depending on the mountings.
A 6-inch lens in a conventional single-motor camera obscura can be designed, built and installed for roughly $8000 to $15,000.
On a larger scale, a fully motorized unit with a 6-inch to 8-inch lens and mirror might cost between $30,000 to $50,000. International customers need to consider costs for shipping and assume any taxes or fees imposed by their country.
Be aware that these cost considerations are only rough estimates and subject to change.